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Worksite Cancer Screening and Nutrition Intervention for High-Risk Auto Workers: Design and Baseline Findings of the Next Step Trial
26, 227–235 (1997) PM960132
PREVENTIVE MEDICINE ARTICLE NO.
Worksite Cancer Screening and Nutrition Intervention for High-Risk Auto Workers: Design and Baseline Findings of the Next Step Trial1 BARBARA C. TILLEY, PH.D.,*,2 SALLY W. VERNON, PH.D.,† KAREN GLANZ, PH.D., M.P.H.,‡ RONALD MYERS, PH.D., D.S.W.,§ KRISTINE SANDERS, M.S., R.D.,¶ MEI LU, PH.D.,* KATHRYN HIRST, PH.D.,* ALAN R. KRISTAL, DR.P.H.,\ CORINNE SMEREKA, M.A.,** AND MARY FRAN SOWERS, PH.D.†† *Division of Biostatistics and Research Epidemiology, Henry Ford Health Sciences Center, Detroit, Michigan 48202; †Behavioral Sciences and Epidemiology, The University of Texas Houston Health Science Center School of Public Health, Houston, Texas 77225; ‡Cancer Research Center of Hawaii, University of Hawaii, Honolulu, Hawaii 96822; §Department of Medicine, Division of Neoplastic Disease, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107; ¶Center for Health Promotion and Disease Prevention, Henry Ford Health System, Detroit, Michigan 48202; \University of Washington, Associate Member, Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, Seattle, Washington 98195; **Better Business Practice, Paramount Communications, Farmington Hills, Michigan 48334; and ††School of Public Health, University of Michigan, Ann Arbor, Michigan 48109
Background. This article describes the design and baseline findings of The Next Step Trial, a health promotion intervention targeting automobile industry employees at increased colorectal cancer risk. The intervention encouraged colorectal cancer screening participation and adoption of low-fat, high-fiber diets. Methods. Twenty-eight worksites (n = 5,042) were randomized to control (a company- sponsored screening program) or intervention (an enhanced screening program including a personalized educational booklet and motivational telephone call and diet-change program including nutrition classes, self-help materials, and computer-generated personalized feedback). Outcomes included screening compliance and fat and fiber intake. Results. Pretrial data indicated targeted employees were predominantly older, well educated, married, Caucasian men. Sixty-one percent (SE = 2) participated in the screening program in the preceding 2 years, and 24% (SE = 1) reported a history of colorectal polyps or cancer. Fifty-eight percent of the cohort responded to the baseline questionnaire; respondents were older and more educated; more were married, retired, and Caucasian than nonrespondents. Mean dietary intakes were 36.9% energy from fat (SE = 0.21), 8.8 g fiber/1,000 kcal (SE = 0.07), and 3.4 servings of fruits and vegetables per day (SE = 0.04). Conclusions. Baseline data show moderate screening participation and dietary intakes that did not meet guidelines; hence intervention efforts were war1 This trial was funded by the National Cancer Institute, Grant CA52605. 2 To whom correspondence and reprint requests should be addressed at the Division of Biostatistics and Research Epidemiology, 1 Ford Place, 3E, Detroit, MI 48202-3450. Fax: (313) 874-6730; Email: [email protected].
ranted. Data from this trial will support a rigorous test of whether this high-risk employee population is responsive to targeted health promotion, early cancer detection, and prevention interventions. © 1997 Academic Press
Key Words: clinical trial; worksites; health promotion; colorectal cancer; nutrition. INTRODUCTION
Colorectal cancer, the second most common cancer among men and women combined, affects approximately 1 in 20 persons in the United States [1]. Recent studies support the effectiveness of screening with fecal occult blood testing [2] and with flexible sigmoidoscopy [3] to reduce colorectal cancer mortality. Many studies suggest that diet changes, in particular reducing fat and increasing fiber, fruits, and vegetables, may reduce colorectal cancer incidence [1,4–8]. In this article we describe the design and baseline findings of The Next Step Trial, a study to promote colorectal cancer screening and diet change targeting automotive pattern and model makers, an occupation with an increased risk of colorectal cancer [9]. The Next Step Trial tests the following primary hypotheses: (1) screening compliance over the 2-year study period in intervention worksites will be higher than screening compliance in control worksites and (2) at the end of the first year of follow-up, intervention worksites will have a lower fat intake and higher fiber intake than control worksites. The trial began data collection in February 1993 and is in the last stages of data collection (verification of employee reports of screening examinations); final analyses are in progress. Based on analyses of baseline data, we present baseline demographics, health, and lifestyle characteristics
227 0091-7435/97 $25.00 Copyright © 1997 by Academic Press All rights of reproduction in any form reserved.
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of the study’s intervention and control worksites and compare characteristics of respondents and nonrespondents to a baseline survey. We present baseline data on colorectal cancer screening, dietary intake, and attitudes and beliefs about screening and nutrition from the baseline survey. Finally, we describe the implications of the baseline findings to future analyses of trial results. While other worksite programs [10–13] have been designed to evaluate nutrition-related cancer prevention and early detection programs separately, the effects of combined primary and secondary colorectal cancer prevention interventions among workers at known increased cancer risk have rarely been investigated. BACKGROUND
An article in the Detroit Free Press in 1979 suggested that automobile manufacturing plant employees from the pattern- and model-making areas were at increased risk of colon cancer [14]. In 1980 the automobile manufacturer in this study began offering periodic screening to at-risk employees (henceforth called the screening program). The screening program included flexible sigmoidoscopy, a digital rectal examination, and a fecal occult blood test. Employees with abnormal findings on screening examinations were referred to their physician for further workup and care. The program targeted active employees, employees on layoff, and retirees who worked at least 2 years at a minimum of 20% time in the pattern- and model-making areas. Plants were located in Michigan, Ohio, Indiana, New York, and Pennsylvania. In 1984, the Division of Biostatistics and Research Epidemiology at the Henry Ford Health Sciences Center became the epidemiologic and statistical center for screening program evaluation. Analyses of findings from the screening program [9] concurred with previous reports of an increased colorectal cancer risk [15– 17]. In 1987, the Occupational Health Advisory Board to the National Joint Committee of the automobile manufacturing company advised the manufacturer to continue offering a colorectal cancer screening program for all employees (active and retired) from the patternand model-making areas. The manufacturer agreed, but by 1989 less than 35% of the eligible employees were participating on a regular basis. In an attempt to learn how to better deliver health promotion programs to this high-risk population, the National Cancer Institute (NCI) funded The Next Step Trial. RESEARCH METHODS
Design and Setting The Next Step Trial was a randomized trial of a multifactor cancer control program to increase colorectal cancer screening and promote healthful dietary behav-
ior. The trial was conducted in 28 worksites participating in the screening program described above, targeting the same employees. The Next Step Trial statistical center provided all worksites with a list of eligible employees, the dates these employees were due for screening, and the type of screening procedures recommended according to American Cancer Society guidelines. All worksites contacted employees to offer screening using procedures already established at each site. The screening program subsumed a group of employees who, in other settings, would be considered under surveillance. This subgroup included those who had previously detected polyps or colorectal cancer and who were followed more intensively. Prior to beginning the trial, concepts for the screening and nutrition interventions were presented to focus groups of employees from the participating worksites (two groups for screening and two for nutrition). The interventions were then pilot tested in the pattern- and model-making areas of four plants that were ineligible for the trial, i.e., had less than 45 employees. The focus group and pilot testing led to a revised intervention, more targeted to the needs of employees [18]. Worksites (self-contained buildings with lunchrooms) rather than individuals were randomly assigned to intervention or control groups. Randomization was stratified where possible on geographic location, number of employees to be screened, and work type (foundry or other). Those worksites with fewer than 45 employees were excluded from the trial. After the completion of 2 years of data collection, in the final year of study funding, the control worksites were offered the intervention. Figure 1 summarizes the trial design. Intervention Strategies Care was taken to make explicit the collaborative nature of the research initiative in the intervention materials. That is, the study and related screening and nutrition intervention materials were presented as being supported by the union, the Henry Ford Health System, and the manufacturer. Screening promotion program. The screening promotion program was developed from theoretical models of behavior change including social cognitive theory [19], the theory of reasoned action [20], and the health belief model [21,22]. The program consisted of a screening invitation mailed to employees in the intervention worksites with an educational booklet (ColoRecord) personalized for the recipient. The educational booklet explained the screening procedures (i.e., fecal occult blood testing, digital rectal examination, and flexible sigmoidoscopy), presented cancer statistics from the ongoing screening program, and included a personalized screening schedule. During a companion telephone call, a counselor reviewed the ColoRecord with
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FIG. 1.
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Design of The Next Step Trial.
the employee, highlighting information about colorectal cancer risk factors, incidence, mortality and survival, screening rationale, examination procedures, and the employee’s personal screening schedule. The counselor encouraged employees to use the ColoRecord booklet when arranging a screening appointment and to direct further questions to worksite medical staff. This intervention was repeated in the second year of the trial. Nutrition education program. The nutrition intervention was based primarily on concepts from social cognitive theory [19], social support principles of adult learning theory [23,24], and the transtheoretical model of behavior change [25]. The intervention consisted of worksite classes and posters, self-help materials, and personalized feedback from food frequency questionnaires. The classes were adapted from ‘The Leaner Weigh to Low-Fat, High-Fiber Fare’, a weight control/ cholesterol reduction program created by the National Center for Health Promotion [26], which emphasizes decreasing total fat intake and increasing dietary fiber. Classes were offered on work time during the first year of the trial to employees in the intervention worksites and their spouses or close friends. Employees were encouraged to share the class manual with household members. One month after the nutrition classes ended, selfhelp materials, entitled ‘‘Taking Charge: Diet and Cancer,’’ were mailed to the homes of employees in the intervention worksites. These materials were previously tested in a self-help nutrition intervention trial in primary care practices [27]. Adding the self-help materials brought the nutrition messages to those at the worksite who chose not to attend classes and to retirees. Adding the self-help materials to the class enhanced the learning experience for those who find auditory learning more difficult than visual learning and, in general, reinforced the message. Employees in both
intervention and control worksites who completed a baseline food frequency received a letter describing their total energy, percentage of energy from fat, and grams of fiber. In the second year of the trial, the nutrition intervention encouraged maintenance of first year gains and encouraged continued dietary change. Using data from the first year’s food frequency, project staff sent respondents in the intervention worksites a quantitative comparison of their diets to the recommendations (based on an adaptation of the U.S. Department of Agriculture’s Food Guide Pyramid) [28] and a series of messages based on their stage of change in adopting a low-fat and high-fiber diet [29,30]. Nonrespondents to the food frequency questionnaire received a generic message. Employees in control sites received the same letter as described for baseline, based on the first year’s dietary data. In the second year of the trial, cafeterias in each intervention worksite displayed posters and brochures relaying simple messages about low-fat, high-fiber eating, changing the messages monthly. Cafeteria food choices coincided with the message for the month. Newsletters. A quarterly newsletter, mailed to homes of intervention-site employees, promoted and reinforced intervention strategies. Newsletter articles highlighted new developments in cancer screening and nutrition and project updates, and included interviews with employee role models [19]. Data Collection Knowledge, attitudes, and beliefs (KAB) survey. At baseline, employees were asked to complete a mailed survey assessing their knowledge, attitudes, and beliefs about colorectal cancer screening and nutrition, readiness to engage in dietary change, and history of screening in the previous year. Items in the screening-
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related section of the survey reflected theoretical constructs associated with cancer screening and dietary practices [31–33] and were adapted from questionnaires used in previous cancer prevention and control studies [34–36]. Scales and single items were used to assess screening-related KAB constructs including salience and coherence, intention, self-efficacy, perceived susceptibility, and worries or fears about the consequences of screening; single items were used to measure the social influence of family members, beliefs about whether colorectal cancer can be prevented and cured, and concern about screening discomfort [37]. Items in the nutrition component of the survey were derived from a Working Well Trial questionnaire [38]. Items were chosen to profile knowledge and beliefs and stage of change separately for fat and fiber. Stages of change represent employees’ current perceptions of their willingness to reduce fat and increase fiber consumption [29,30]. The KAB survey was mailed at baseline with a metered return envelope. Incentive gifts (e.g., pocket screwdriver, pocket knife, nylon lunch bag) were included with surveys in all years. Nonrespondents were reminded by postcard after 2 weeks and then called after 4 weeks and prompted to return the survey. Food frequency questionnaire (FFQ). A FFQ was sent out with the KAB survey at baseline and at Years 1 and 2 to collect data on fat, fiber, fruit, and vegetable intake. The FFQ, designed at Fred Hutchinson Cancer Research Center, is a modification of the NCI Health Habits and History Questionnaire developed by Block and others [39], and has been tested and validated in self-administered format [40]. The nutrient database is derived from the University of Minnesota Nutrition Coding Center’s Diet Analysis System [41], and algorithms for analyzing this FFQ are described elsewhere [42].
survey nonrespondents with data from survey respondents will allow assessment of response bias. Quality assurance. Evaluation of the data collection process occurred throughout the trial and included monitoring the follow-up calls for the ColoRecord, calls to nonrespondents, data collection activities, and nutrition classes. Extensive range and consistency checks were run on the data. Items on the KAB with more than one answer were identified and recoded according to a prespecified algorithm. In the FFQ, multiple marks, incomplete forms, and out of range dates or ID numbers were corrected or returned to the employee to be corrected. After the nutrients were calculated, those with daily energy intakes less than 600 or more than 5,000 were excluded from further analyses. For the screening data, dates of physical examinations from various sources (plant, physician report, employee selfreport) were compared and discrepancies were resolved. Definitions and Measurement of Trial Primary Outcomes Screening compliance. An eligible employee will be considered compliant if the employee presents for a screening examination (i.e., digital rectal examination, fecal occult blood test, and/or flexible sigmoidoscopy) in both the first and the second year of the trial. An employee who has no examination recommended in either year will be counted as compliant. Dietary intake. FFQ data will be used to calculate the percentage energy from fat and fiber intake per 1000 kilocalories for an individual. Sample Size
Screening. Yearly, data on screening participation were provided to The Next Step statistical center by worksite staff and through self-reports on the KAB survey. Data on physical examination results were provided by worksite staff or by the employees’ physicians (with the employees’ consent).
Sample size estimates were based on the need for a sufficient number of worksites to study both the primary screening and the primary nutrition outcome. Sample size calculations were based on methods described by Donner et al. [44] for clustered designs. (In this trial, the worksites were the clusters.) An average worksite size of 100 was used to adjust for the unequal number of employees in the worksite.
Follow-up data. Follow-up surveys at the end of the first and second years of the trial were mailed with a stamped return envelope in hopes of increasing response rates [43]. Additional data on screening participants were collected by telephone from survey nonrespondents at the end of the first year of the trial. Also, at the end of the first year selected items from the screening and nutrition sections of the KAB and FFQ were collected by telephone. In addition, nonrespondents were queried about smoking and their marital and retirement statuses. Comparing data collected at the end of the first and second years by telephone from
Screening outcome. In calculating sample size estimates for screening, the control rate for compliance was based on the observed initial 34% compliance (percentage of employees participating in all three of the first three screens, 1980–1984). In this trial, compliance would be measured over two periods (1993–1995) rather than three, but a decrease in compliance was expected over time, so 34 percent was considered a reasonable estimate. Cornfield’s approach [45] was used to calculate the variance inflation factor. The betweenworksite variance was estimated to be 0.033 and the inflation factor 26.49. A difference of 23% could be de-
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tected with power greater than 0.9, a 4 0.05, two-sided test. Fat and fiber outcomes. The between-worksite variance for total fiber was estimated to be 3.72 and the total variance 60.95. For both fiber and fat, the inflation factor, the ratio of the between-worksite variance to the total variance, was estimated from the earlier (pretrial) screening data. Given the sample size, a mean increase in total fiber of 5 g could be detected with power greater than 0.9, a 4 0.05, two-sided test. The between-worksite variance for total fat was estimated to be 124.8 and the total variance 1,308.8. Given the sample size, a mean decrease in total fat of 9 g could be detected with power greater than 0.9, a 4 0.05, two-sided test. Total fat was used to estimate power because preliminary data on percentage of calories from fat were not available. Final sample size. The study sample size was 28 worksites including a total of 5,042 employees at baseline. The planned analyses using more complex models than those proposed by Donner et al. [44] should increase the power to detect differences with this sample size. Statistical Analysis Analysis approach. Standard errors given in this report and the comparison of characteristics of survey respondents and nonrespondents and intervention and control groups are computed taking the worksite clustering into account [46]. Generalized estimating equations [47] were used to take the correlations within worksite into account when adjusting for covariates in comparing responders and nonresponders. Intention to treat. In general, randomized clinical trials follow the accepted principle that participants should be analyzed in the treatment group to which they are assigned, regardless of postrandomization occurrences [48,49]. In a trial where the unit of analysis is the worksite and where there is in-and-out migration of workers and between-site transfers, application of the intention-to-treat principle is not straightforward. For this trial, participants in the primary analyses: (1) satisfy eligibility requirements to receive the survey mailing in the year being analyzed (worked in the pattern- and model-making area and were currently actively employed, retired, or on layoff) and (2) are assigned to the worksite they were associated with when they entered the trial. For analyses of screening compliance, an employee with missing data will be considered a noncomplier. Primary analyses of fat and fiber intake will be restricted to those completing a FFQ either at baseline or at 1 year. Missing values for those who completed the baseline FFQ but were nonrespondents to the survey
in the first year will be imputed using the first-year site mean for those of the same gender and retirement status. For those employees completing a FFQ in the first year, but missing a baseline FFQ, baseline nutrient intake values will be imputed from the baseline site mean for those of the same gender and retirement status . As an ancillary analysis of fiber and fat intake, analyses will be conducted without imputation, excluding those who do not have both a FFQ at baseline and Year 1. This approach is similar to that used in CATCH [50], where the clusters were elementary schools, with the exception that CATCH did not allow for migration into the site, as was necessary for this trial. RESULTS
The tables to follow describe the intervention and control groups’ baseline characteristics, compare respondents and nonrespondents to the baseline survey, and describe baseline survey findings for survey respondents. Table 1 gives employee characteristics by intervention and control worksites. The cohort is predominantly male and Caucasian. In contrast to other worksite programs, because both former and current TABLE 1 Comparison of Baseline Characteristics of Intervention and Control Worksites
Characteristic
Fifteen intervention worksites n 4 2,240
Thirteen control worksites n 4 2,802
P valuea
54 (0.70) 95 (1) 33 (2) 85 (2) 95 (1)
57 (0.75) 97 (1) 43 (3) 85 (1) 94 (1)
0.01 0.18 0.001 0.96 0.48
10 (1) 32 (2) 32 (2) 26 (2)
16 (2) 32 (1) 30 (1) 23 (2)
18 (1) 27 (0.11)
20 (1) 27 (0.11)
0.11 1.00
60 (4)
62 (2)
0.77
21 (2) 61 (3)
27 (1) 55 (2)
0.01 0.13
b
Demographics Age, mean (SEa), years Male, percent (SE) Retired, percent (SE) Married, percent (SE) Caucasian, percent (SE) Educationc (SE) <12 years 12 years 13–15 years ù16 years Lifestyle and health history Smoked cigarettes within 1 year of baseline,d percent (SE) Body mass index, mean (SE) Screened at least once in the 2 years prior to baseline (pretrial coverage) (SE) History of polyps of colorectal cancere (SE) Response to baseline survey
0.19
a Weighted means, standard errors and P values computed using ratio estimates to summarize across worksites adjusting for clustering within worksite. b 63 were missing ethnicity, 92 were missing years of education, and 33 were missing marital status. c Includes trade school. The statistical test was based on the continuous distribution of education. d 3,669 employees responded to the smoking question. Smoking information came from the baseline survey or from a health history questionnaire within a year of the baseline survey or from the 1-year survey. e From a physical examination report, pathology report, or employee selfreport.
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employees were eligible to participate, 39% (SE 4 2) were retired. Employees in the control worksites were older (P 4 0.01), more likely to be retired (P 4 0.001), and more likely to have a previous history of colorectal cancer or polyps (P 4 0.01) than employees in intervention worksites. There was no detectable difference in the proportion screened at least once in the 2 years prior to baseline (P 4 0.77). The overall response rate to the baseline survey was 58% (SE 4 2), ranging from 47 to 84% across the 28 worksites. No significant differences were found in crude response rates between the intervention and control worksites (Table 1). Table 2 gives the baseline demographic and healthrelated characteristics of respondents and nonrespondents to the baseline survey. Compared with nonrespondents, respondents were older and more likely to be Caucasian, male, married, retired, and better educated and less likely to be smokers (Table 2). They were more likely to have been screened in the preceding 2 years and also were more likely to have a personal history of colorectal cancer or polyps. Although body mass index was statistically significant, the difference in observed mean scores was minimal. Analyses by plant showed consistency across worksites in the com-
TABLE 2 Baseline Characteristics of Responders and Nonresponders to The Next Step Trial Baseline Survey FFQ or KAB survey
Characteristic Demographicsb Age, mean (SE) a years Male, percent (SE) Retired, percent (SE) Married, percent (SE) Caucasian, percent (SE) Education,c percent (SE) <12 years 12 years 13–15 years 16–18 years Lifestyle and health history Smoked cigarettes within 1 year of baselined percent (SE) Body mass index (SE) Screened at least once in the 2 years prior to baseline (pretrial coverage) (SE) History of polyps or colorectal cancer,e percent (SE) a
Responders (n 4 2,926)
Nonresponders (n 4 2,116)
P valuea
57 (0.59) 98 (0.2) 44 (2) 88 (1) 96 (1)
53 (0.84) 93 (1) 31 (2) 81 (2) 91 (1)
<0.001 <0.001 <0.001 <0.001 <0.001
10 (1) 31 (1) 30 (2) 28 (2)
17 (2) 33 (2) 31 (1) 20 (2)
18 (1) 27 (0.08)
23 (1) 27 (0.22)
<0.001 0.04
76 (2)
40 (3)
<0.001
30 (2)
17 (2)
<0.001
0.003
Weighted means, standard errors, and P values computed using ratio estimates to summarize across worksites adjusting for clustering within worksite. b 63 were missing ethnicity, 92 were missing years of education, and 33 were missing marital status. c Includes trade school. d 3,669 employees responded to the smoking question. Smoking information came from the baseline survey or from a health history questionnaire within a year of the baseline survey or from the 1-year survey. e From the physical examination report, pathology report, or patient report.
parisons of respondents and nonrespondents on these baseline characteristics. Table 3 gives baseline survey data for the total cohort of survey respondents by intervention and control worksites. No significant differences were found between intervention and control worksites for 9 of the 10 screening-related attitudinal scales from the KAB survey using P ø 0.10 as the critical level. Among survey responders, the intervention group was less likely to express belief in prevention of colorectal cancer. No significant differences were found between intervention and control worksites on the nutrition-related variables. Of survey respondents, 42% (SE 4 1) were in the action stage of change for adopting a low-fat diet, and 29% (SE 4 1) considered themselves to be maintaining a low-fat diet. Overall, respondents (28%, SE 4 1) were in the action stage of adopting a high-fiber diet, although more (37%, SE 4 1) considered themselves to be maintaining a high-fiber diet. In the total cohort, fat intake was relatively high (36.9% energy from fat, SE 4 0.2), and both fiber intake (8.8 g/1,000 kcal, SE 4 0.1) and fruit and vegetable intake (3.4 servings/day, SE 4 0.04) were moderate. Only 17% of respondents ate less than 30% energy from fat, 14% reported a diet with 12 or more grams of fiber/1,000 kcal, and 18% reported eating five or more servings of fruits and vegetables per day. DISCUSSION
The Next Step Trial was similar in design to recent worksite health promotion trials such as Working Well [11], Treatwell [12], and Five A Day [51] in that worksites, rather than individuals, were randomized to intervention or control groups. The Next Step Trial was different, however, in that it focused on colorectal cancer screening and targeted only employees at high risk for colorectal cancer. Employees in our study had been made aware of their increased risk through a newspaper article [19], the article by Tilley et al. [9], their union, and the plant medical staff who promoted the ongoing cancer screening program. Thus, this trial offers a special opportunity to evaluate a health and screening program in a group where the intervention can be linked to defined and recognized risk. The trial also is unique because it includes both active and retired employees and because it addresses both primary and secondary cancer prevention through a combination of interventions aimed at nutrition and screening. Because the screening intervention was added to an existing worksite screening program, the trial will assess the additive effect of a behavioral intervention on screening participation in an ongoing screening program. No structured cancer-related nutrition intervention was in place at the time the trial began; so, we will be able to test the impact of a de novo nutrition intervention.
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TABLE 3 Responders to The Next Step Trial Baseline Survey on Attitudes and Beliefs about Colorectal Cancer Screening and Nutrition Fifteen intervention worksites n 4 1,362
Thirteen control worksites n 4 1,541
P valueb
3.55 (0.02) 3.42 (0.04) 3.10 (0.03) 2.43 (0.03) 3.05 (0.03) 2.56 (0.03) 3.51 (0.02) 3.26 (0.02) 2.95 (0.03) 3.22 (0.03)
3.56 (0.02) 3.44 (0.02) 3.13 (0.03) 2.42 (0.03) 3.09 (0.02) 2.64 (0.05) 3.55 (0.02) 3.34 (0.02) 3.02 (0.04) 3.24 (0.03)
0.61 0.73 0.45 0.74 0.18 0.13 0.18 0.005 0.19 0.76
10 (0.4) 16 (1) 2 (0.3) 44 (1) 29 (1)
10 (0.4) 18 (1) 2 (0.3) 40 (1) 30 (1)
0.26
a
Screening attitudes and beliefs Salience and coherence, mean (SE)b Intention, mean (SE) Self-efficacy, mean (SE) Perceived susceptibility, mean (SE) Worries, mean (SE) Screening discomfort, mean (SE) Belief that colorectal cancer can be cured, mean (SE) Belief in prevention, mean (SE) Wants to do what family thinks about screening, mean (SE) Family thinks employee should be screened, mean (SE) Nutrition—stages of changea Fat consumption stages of change,d percentage of respondents • Precontemplation • Contemplation • Preparation • Action • Maintenance Fiber consumption stages of change,c percentage of repondents • Precomtemplation • Contemplation • Preparation • Action • Maintenance Nutrient intake (FFQ) Energy intake, mean (SE) Fat (percentage energy), mean (SE) Fiber (g/1,000 kcal), mean (SE) Servings of fruits per day,d n 4 2796, mean (SE) Servings of vegetables per day,d n 4 2794, mean (SE) Servings of fruits and vegetables per day,d n 4 2790, mean (SE)
7 (0.8) 25 (1) 4 (1) 28 (1) 37 (1) n 4 1,369 1,783 (22) 37.2 (0.3) 8.8 (0.1) 1.6 (0.04) 1.7 (0.04) 3.4 (0.05)
7 (0.3) 23 (1) 4 (0.4) 29 (1) 37 (1) n 4 1,541 1,735 (21) 36.7 (0.2) 8.9 (0.1) 1.6 (0.04) 1.7 (0.02) 3.4 (0.06)
0.66
0.11 0.23 0.75 0.79 0.73 0.72
a From KAB (survey on knowledge, attitudes and beliefs about screening and nutrition). For the screening variables, scale is 1–5 (strongly disagree to strongly agree). FFQ, food frequency questionnaire. n’s represent the number of employees responding to the survey. Nonrespondents are excluded. b Weighted means, standard errors, and P values computed using ratio estimates to summarize across worksites adjusting for clustering within worksite. c 97 employees responded with insufficient information to be staged for fat and 90 to be staged for fiber. d Fruits, sum of response to ‘‘how often did you eat fruit, not counting juices’’ and FFQ item on juices. Vegetables, sum of the response to ‘‘how often did you eat vegetables, not including salad or fried potatoes?’’ and two FFQ items on ‘‘green salad’’ and ‘‘potatoes, including boiled, baked, mashed and potato salad.’’ Fruits and vegetables, sum of two items. Missing data are determined by nonresponse and by a FFQ algorithm for errors. Statistical test was done on log transformation.
From the baseline analyses, we learned that pretrial coverage (screening at least once in the 2 years preceding baseline in 1993) was 61% in our study population prior to initiation of the enhanced screening intervention [9]. This figure is substantially higher than the 34% observed in a similar worksite program [52] offered over a 4-year interval. However, consistent with the sample size assumption, i.e., that participation would decrease over time, pretrial coverage in 1993 was less than the 79% coverage (screening at least once in first three cycles of the program) that we observed in our study population in 1989 [9]. These data on coverage suggest that while there is a decrease in participa-
tion over time, many in the cohort remained willing to participate in the screening program prior to the introduction of the behavioral intervention. The baseline survey response rate of 58% was similar to other studies using mailed food frequencies [53]. The Next Step Trial response rate was in line with the 61% response rate observed in the Working Well Trial in those worksites that administered the questionnaires by mail. In the Working Well Trial some worksites increased response rates by group administration of questionnaires during work time [11,54], an approach not possible in The Next Step Trial due to costs to the employer and the location of retirees off-site.
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Studies conducted at the worksite, particularly those relying on questionnaire data to measure study outcomes, would benefit from collecting data on-site. We found that respondents and nonrespondents to the FFQ and KAB baseline questionnaire differed significantly in terms of sociodemographic characteristics, medical history, and past screening behavior. The pattern of response was similar to that observed by Lerman and Shemer [55] who reported that respondents to health promotion programs tended to be people already committed to healthy life styles and by Lindsted et al. [56] who found that survey responders showed decreased mortality in the first few years after a survey. The intervention and control worksites differed in age, retirement status, and history of colorectal cancer and polyps. Although some of the intervention and control group differences were statistically significant, the magnitude of these differences was small. Given the large number of worksites, the large size of the total cohort, and the ability of the chosen statistical methods to adjust for covariates, we believe meaningful comparisons between the intervention and the control groups can be made. It is important to acknowledge that the generalizability of nutrition intervention results may be limited by respondent/nonrespondent differences because results will be based on survey data. However, given the randomized design, we concluded that comparison of intervention and control worksites would not be biased unless there was a differential response to the survey between intervention and control sites, a situation that did not occur. Our conclusion is consistent with that of Lindsted et al. [56]. In the Adventist health cohort study, their results suggested that, in general, for internal comparisons, no bias is likely to occur due to the healthy volunteer effect. The screening intervention is more likely to be generalizable to similar settings because compliance is measured both by survey data and by medical records. However, based on survey responses, control and intervention worksites did differ on one attitudinal measure related to screening effectiveness. Because we do not have survey data on all study participants, we will adjust for potential screening-related attitudinal differences between intervention and control worksites in primary analyses by controlling for recent screening behavior, a variable that is available on all employees and that indicates a predisposition toward preventive health behaviors. In conclusion, data from this trial will support a rigorous test of whether this high-risk employee population is responsive to targeted health promotion, early cancer detection, and prevention interventions. We believe that these data will be useful in planning health promotion programs for other high-risk groups.
ACKNOWLEDGMENTS The authors thank Donna Mott and Toni Chociemski for assistance with computer programming, Michele Small and Mary Ann Kozlowski for data management support, and the interviewing and abstracting team, headed by Lois Lamerato, for their support throughout the trial. REFERENCES 1. Cohen AM, Shank B, Friedman MA. Colorectal cancer. In: DeVita VT, Hellmana S, Rosenberg AS, editors. Cancer: principles and practice of oncology, 3rd ed. Philadelphia: Lippincott, 1989: 895–964. 2. Mandel JS, Bond JH, Church TR, Snover DC, Bradley GM, Schuman LM, et al. Reducing mortality from colorectal cancer by screening for fecal occult blood. N Engl J Med 1993;328:1365–71. 3. Selby JV, Friedman GD, Quensenberry CP, Weiss NS. A case– control study of screening sigmoidoscopy and mortality from colorectal cancer. N Engl J Med 1992;326:653–7. 4. Greenwald P, Sondik E. Cancer control objectives for the nation, 1985–2000. Washington: National Cancer Institute, 1986; NCI Monogr., HDDS Publication (PHS). 5. Graham S, Marshall J, Haughey B, Mittelman A, Swanson MYA, Zielezny M, et al. Dietary epidemiology of cancer of the colon in western New York. Am J Epidemiol 1988;128:490–503. 6. Trock B, Lanza E, Greenwald P. Dietary fiber, vegetables, and colon cancer: critical review and meta-analyses of the epidemiologic evidence. J Natl Cancer Inst 1990;82:650–61. 7. Kolonel LN, LeMarchand L. The epidemiology of colon cancer and dietary fat. In: Anonymous. Dietary fat and cancer. New York: A. R. Liss, 1986:69–91. 8. Willett WC, Stampfer MJ, Colditz GA, Rosner BA, Speizer FE. Relation of meat, fat and fiber intake to the risk of colon cancer in a prospective study among women. N Engl J Med 1990; 323: 1664–72. 9. Tilley BC, Johnson CC, Schultz LR, Buffler PA, Joseph CLM. Risk of colorectal cancer among automotive pattern and model makers. J Occup Med 1990; 32:541–6. 10. Sorensen G, Himmelstein JS, Hunt MK. A model for worksite cancer prevention: integration of health protection and health promotion in the Well Works Project. Am J Health Promo. 1995;10:55–62. 11. Abrams DB, Boutwell WB, Grizzle J, Heimendinger J, Sorensen G, Varnes J. Cancer control at the workplace: the Working Well Trial. Prev Med 1994;23:15–27. 12. Sorensen G, Morris DM, Hunt MK, Herbert JR, Harris DR, Staddard A, et al. Work-site nutrition intervention and employees’ dietary habits: the Treatwell Program. Am J Public Health 1992;82:877–80. 13. Glanz K, Rimer B, Lerman C, Gorchov P. Factors influencing acceptance of mammography: implications for enhancing worksite cancer control. Am J Health Promo 1992;7:28–36. 14. Anonymous. Cancer study sought for auto wood shops. Detroit Free Press, Nov. 7, 1979. 15. Ibrahim MAH, Batra SK, Schuman BM, Viola FV. Fiberoptic sigmoidoscopy in screening pattern makers for colon cancer at their work place. Am J Gastroenterol 1984;79:262–4. 16. Demers RY, Demers P, Hoar SK, Deighton K. Prevalence of colorectal polyps among Michigan pattern and model makers. J Occup Med 1985; 27:809–12. 17. Hoar SK, Bang KM, Tillet S, Rodriguez M, Cantor KP, Blair A. Screening for colorectal cancer and polyps among pattern makers. J Occup Med 1986;28:704–8. 18. Tilley B, Vernon S, Myers R, Glanz K, Lu M, Sanders K, et al.
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PREVENTIVE MEDICINE ARTICLE NO.
Worksite Cancer Screening and Nutrition Intervention for High-Risk Auto Workers: Design and Baseline Findings of the Next Step Trial1 BARBARA C. TILLEY, PH.D.,*,2 SALLY W. VERNON, PH.D.,† KAREN GLANZ, PH.D., M.P.H.,‡ RONALD MYERS, PH.D., D.S.W.,§ KRISTINE SANDERS, M.S., R.D.,¶ MEI LU, PH.D.,* KATHRYN HIRST, PH.D.,* ALAN R. KRISTAL, DR.P.H.,\ CORINNE SMEREKA, M.A.,** AND MARY FRAN SOWERS, PH.D.†† *Division of Biostatistics and Research Epidemiology, Henry Ford Health Sciences Center, Detroit, Michigan 48202; †Behavioral Sciences and Epidemiology, The University of Texas Houston Health Science Center School of Public Health, Houston, Texas 77225; ‡Cancer Research Center of Hawaii, University of Hawaii, Honolulu, Hawaii 96822; §Department of Medicine, Division of Neoplastic Disease, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107; ¶Center for Health Promotion and Disease Prevention, Henry Ford Health System, Detroit, Michigan 48202; \University of Washington, Associate Member, Cancer Prevention Research Program, Fred Hutchinson Cancer Research Center, Seattle, Washington 98195; **Better Business Practice, Paramount Communications, Farmington Hills, Michigan 48334; and ††School of Public Health, University of Michigan, Ann Arbor, Michigan 48109
Background. This article describes the design and baseline findings of The Next Step Trial, a health promotion intervention targeting automobile industry employees at increased colorectal cancer risk. The intervention encouraged colorectal cancer screening participation and adoption of low-fat, high-fiber diets. Methods. Twenty-eight worksites (n = 5,042) were randomized to control (a company- sponsored screening program) or intervention (an enhanced screening program including a personalized educational booklet and motivational telephone call and diet-change program including nutrition classes, self-help materials, and computer-generated personalized feedback). Outcomes included screening compliance and fat and fiber intake. Results. Pretrial data indicated targeted employees were predominantly older, well educated, married, Caucasian men. Sixty-one percent (SE = 2) participated in the screening program in the preceding 2 years, and 24% (SE = 1) reported a history of colorectal polyps or cancer. Fifty-eight percent of the cohort responded to the baseline questionnaire; respondents were older and more educated; more were married, retired, and Caucasian than nonrespondents. Mean dietary intakes were 36.9% energy from fat (SE = 0.21), 8.8 g fiber/1,000 kcal (SE = 0.07), and 3.4 servings of fruits and vegetables per day (SE = 0.04). Conclusions. Baseline data show moderate screening participation and dietary intakes that did not meet guidelines; hence intervention efforts were war1 This trial was funded by the National Cancer Institute, Grant CA52605. 2 To whom correspondence and reprint requests should be addressed at the Division of Biostatistics and Research Epidemiology, 1 Ford Place, 3E, Detroit, MI 48202-3450. Fax: (313) 874-6730; Email: [email protected].
ranted. Data from this trial will support a rigorous test of whether this high-risk employee population is responsive to targeted health promotion, early cancer detection, and prevention interventions. © 1997 Academic Press
Key Words: clinical trial; worksites; health promotion; colorectal cancer; nutrition. INTRODUCTION
Colorectal cancer, the second most common cancer among men and women combined, affects approximately 1 in 20 persons in the United States [1]. Recent studies support the effectiveness of screening with fecal occult blood testing [2] and with flexible sigmoidoscopy [3] to reduce colorectal cancer mortality. Many studies suggest that diet changes, in particular reducing fat and increasing fiber, fruits, and vegetables, may reduce colorectal cancer incidence [1,4–8]. In this article we describe the design and baseline findings of The Next Step Trial, a study to promote colorectal cancer screening and diet change targeting automotive pattern and model makers, an occupation with an increased risk of colorectal cancer [9]. The Next Step Trial tests the following primary hypotheses: (1) screening compliance over the 2-year study period in intervention worksites will be higher than screening compliance in control worksites and (2) at the end of the first year of follow-up, intervention worksites will have a lower fat intake and higher fiber intake than control worksites. The trial began data collection in February 1993 and is in the last stages of data collection (verification of employee reports of screening examinations); final analyses are in progress. Based on analyses of baseline data, we present baseline demographics, health, and lifestyle characteristics
227 0091-7435/97 $25.00 Copyright © 1997 by Academic Press All rights of reproduction in any form reserved.
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of the study’s intervention and control worksites and compare characteristics of respondents and nonrespondents to a baseline survey. We present baseline data on colorectal cancer screening, dietary intake, and attitudes and beliefs about screening and nutrition from the baseline survey. Finally, we describe the implications of the baseline findings to future analyses of trial results. While other worksite programs [10–13] have been designed to evaluate nutrition-related cancer prevention and early detection programs separately, the effects of combined primary and secondary colorectal cancer prevention interventions among workers at known increased cancer risk have rarely been investigated. BACKGROUND
An article in the Detroit Free Press in 1979 suggested that automobile manufacturing plant employees from the pattern- and model-making areas were at increased risk of colon cancer [14]. In 1980 the automobile manufacturer in this study began offering periodic screening to at-risk employees (henceforth called the screening program). The screening program included flexible sigmoidoscopy, a digital rectal examination, and a fecal occult blood test. Employees with abnormal findings on screening examinations were referred to their physician for further workup and care. The program targeted active employees, employees on layoff, and retirees who worked at least 2 years at a minimum of 20% time in the pattern- and model-making areas. Plants were located in Michigan, Ohio, Indiana, New York, and Pennsylvania. In 1984, the Division of Biostatistics and Research Epidemiology at the Henry Ford Health Sciences Center became the epidemiologic and statistical center for screening program evaluation. Analyses of findings from the screening program [9] concurred with previous reports of an increased colorectal cancer risk [15– 17]. In 1987, the Occupational Health Advisory Board to the National Joint Committee of the automobile manufacturing company advised the manufacturer to continue offering a colorectal cancer screening program for all employees (active and retired) from the patternand model-making areas. The manufacturer agreed, but by 1989 less than 35% of the eligible employees were participating on a regular basis. In an attempt to learn how to better deliver health promotion programs to this high-risk population, the National Cancer Institute (NCI) funded The Next Step Trial. RESEARCH METHODS
Design and Setting The Next Step Trial was a randomized trial of a multifactor cancer control program to increase colorectal cancer screening and promote healthful dietary behav-
ior. The trial was conducted in 28 worksites participating in the screening program described above, targeting the same employees. The Next Step Trial statistical center provided all worksites with a list of eligible employees, the dates these employees were due for screening, and the type of screening procedures recommended according to American Cancer Society guidelines. All worksites contacted employees to offer screening using procedures already established at each site. The screening program subsumed a group of employees who, in other settings, would be considered under surveillance. This subgroup included those who had previously detected polyps or colorectal cancer and who were followed more intensively. Prior to beginning the trial, concepts for the screening and nutrition interventions were presented to focus groups of employees from the participating worksites (two groups for screening and two for nutrition). The interventions were then pilot tested in the pattern- and model-making areas of four plants that were ineligible for the trial, i.e., had less than 45 employees. The focus group and pilot testing led to a revised intervention, more targeted to the needs of employees [18]. Worksites (self-contained buildings with lunchrooms) rather than individuals were randomly assigned to intervention or control groups. Randomization was stratified where possible on geographic location, number of employees to be screened, and work type (foundry or other). Those worksites with fewer than 45 employees were excluded from the trial. After the completion of 2 years of data collection, in the final year of study funding, the control worksites were offered the intervention. Figure 1 summarizes the trial design. Intervention Strategies Care was taken to make explicit the collaborative nature of the research initiative in the intervention materials. That is, the study and related screening and nutrition intervention materials were presented as being supported by the union, the Henry Ford Health System, and the manufacturer. Screening promotion program. The screening promotion program was developed from theoretical models of behavior change including social cognitive theory [19], the theory of reasoned action [20], and the health belief model [21,22]. The program consisted of a screening invitation mailed to employees in the intervention worksites with an educational booklet (ColoRecord) personalized for the recipient. The educational booklet explained the screening procedures (i.e., fecal occult blood testing, digital rectal examination, and flexible sigmoidoscopy), presented cancer statistics from the ongoing screening program, and included a personalized screening schedule. During a companion telephone call, a counselor reviewed the ColoRecord with
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FIG. 1.
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Design of The Next Step Trial.
the employee, highlighting information about colorectal cancer risk factors, incidence, mortality and survival, screening rationale, examination procedures, and the employee’s personal screening schedule. The counselor encouraged employees to use the ColoRecord booklet when arranging a screening appointment and to direct further questions to worksite medical staff. This intervention was repeated in the second year of the trial. Nutrition education program. The nutrition intervention was based primarily on concepts from social cognitive theory [19], social support principles of adult learning theory [23,24], and the transtheoretical model of behavior change [25]. The intervention consisted of worksite classes and posters, self-help materials, and personalized feedback from food frequency questionnaires. The classes were adapted from ‘The Leaner Weigh to Low-Fat, High-Fiber Fare’, a weight control/ cholesterol reduction program created by the National Center for Health Promotion [26], which emphasizes decreasing total fat intake and increasing dietary fiber. Classes were offered on work time during the first year of the trial to employees in the intervention worksites and their spouses or close friends. Employees were encouraged to share the class manual with household members. One month after the nutrition classes ended, selfhelp materials, entitled ‘‘Taking Charge: Diet and Cancer,’’ were mailed to the homes of employees in the intervention worksites. These materials were previously tested in a self-help nutrition intervention trial in primary care practices [27]. Adding the self-help materials brought the nutrition messages to those at the worksite who chose not to attend classes and to retirees. Adding the self-help materials to the class enhanced the learning experience for those who find auditory learning more difficult than visual learning and, in general, reinforced the message. Employees in both
intervention and control worksites who completed a baseline food frequency received a letter describing their total energy, percentage of energy from fat, and grams of fiber. In the second year of the trial, the nutrition intervention encouraged maintenance of first year gains and encouraged continued dietary change. Using data from the first year’s food frequency, project staff sent respondents in the intervention worksites a quantitative comparison of their diets to the recommendations (based on an adaptation of the U.S. Department of Agriculture’s Food Guide Pyramid) [28] and a series of messages based on their stage of change in adopting a low-fat and high-fiber diet [29,30]. Nonrespondents to the food frequency questionnaire received a generic message. Employees in control sites received the same letter as described for baseline, based on the first year’s dietary data. In the second year of the trial, cafeterias in each intervention worksite displayed posters and brochures relaying simple messages about low-fat, high-fiber eating, changing the messages monthly. Cafeteria food choices coincided with the message for the month. Newsletters. A quarterly newsletter, mailed to homes of intervention-site employees, promoted and reinforced intervention strategies. Newsletter articles highlighted new developments in cancer screening and nutrition and project updates, and included interviews with employee role models [19]. Data Collection Knowledge, attitudes, and beliefs (KAB) survey. At baseline, employees were asked to complete a mailed survey assessing their knowledge, attitudes, and beliefs about colorectal cancer screening and nutrition, readiness to engage in dietary change, and history of screening in the previous year. Items in the screening-
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related section of the survey reflected theoretical constructs associated with cancer screening and dietary practices [31–33] and were adapted from questionnaires used in previous cancer prevention and control studies [34–36]. Scales and single items were used to assess screening-related KAB constructs including salience and coherence, intention, self-efficacy, perceived susceptibility, and worries or fears about the consequences of screening; single items were used to measure the social influence of family members, beliefs about whether colorectal cancer can be prevented and cured, and concern about screening discomfort [37]. Items in the nutrition component of the survey were derived from a Working Well Trial questionnaire [38]. Items were chosen to profile knowledge and beliefs and stage of change separately for fat and fiber. Stages of change represent employees’ current perceptions of their willingness to reduce fat and increase fiber consumption [29,30]. The KAB survey was mailed at baseline with a metered return envelope. Incentive gifts (e.g., pocket screwdriver, pocket knife, nylon lunch bag) were included with surveys in all years. Nonrespondents were reminded by postcard after 2 weeks and then called after 4 weeks and prompted to return the survey. Food frequency questionnaire (FFQ). A FFQ was sent out with the KAB survey at baseline and at Years 1 and 2 to collect data on fat, fiber, fruit, and vegetable intake. The FFQ, designed at Fred Hutchinson Cancer Research Center, is a modification of the NCI Health Habits and History Questionnaire developed by Block and others [39], and has been tested and validated in self-administered format [40]. The nutrient database is derived from the University of Minnesota Nutrition Coding Center’s Diet Analysis System [41], and algorithms for analyzing this FFQ are described elsewhere [42].
survey nonrespondents with data from survey respondents will allow assessment of response bias. Quality assurance. Evaluation of the data collection process occurred throughout the trial and included monitoring the follow-up calls for the ColoRecord, calls to nonrespondents, data collection activities, and nutrition classes. Extensive range and consistency checks were run on the data. Items on the KAB with more than one answer were identified and recoded according to a prespecified algorithm. In the FFQ, multiple marks, incomplete forms, and out of range dates or ID numbers were corrected or returned to the employee to be corrected. After the nutrients were calculated, those with daily energy intakes less than 600 or more than 5,000 were excluded from further analyses. For the screening data, dates of physical examinations from various sources (plant, physician report, employee selfreport) were compared and discrepancies were resolved. Definitions and Measurement of Trial Primary Outcomes Screening compliance. An eligible employee will be considered compliant if the employee presents for a screening examination (i.e., digital rectal examination, fecal occult blood test, and/or flexible sigmoidoscopy) in both the first and the second year of the trial. An employee who has no examination recommended in either year will be counted as compliant. Dietary intake. FFQ data will be used to calculate the percentage energy from fat and fiber intake per 1000 kilocalories for an individual. Sample Size
Screening. Yearly, data on screening participation were provided to The Next Step statistical center by worksite staff and through self-reports on the KAB survey. Data on physical examination results were provided by worksite staff or by the employees’ physicians (with the employees’ consent).
Sample size estimates were based on the need for a sufficient number of worksites to study both the primary screening and the primary nutrition outcome. Sample size calculations were based on methods described by Donner et al. [44] for clustered designs. (In this trial, the worksites were the clusters.) An average worksite size of 100 was used to adjust for the unequal number of employees in the worksite.
Follow-up data. Follow-up surveys at the end of the first and second years of the trial were mailed with a stamped return envelope in hopes of increasing response rates [43]. Additional data on screening participants were collected by telephone from survey nonrespondents at the end of the first year of the trial. Also, at the end of the first year selected items from the screening and nutrition sections of the KAB and FFQ were collected by telephone. In addition, nonrespondents were queried about smoking and their marital and retirement statuses. Comparing data collected at the end of the first and second years by telephone from
Screening outcome. In calculating sample size estimates for screening, the control rate for compliance was based on the observed initial 34% compliance (percentage of employees participating in all three of the first three screens, 1980–1984). In this trial, compliance would be measured over two periods (1993–1995) rather than three, but a decrease in compliance was expected over time, so 34 percent was considered a reasonable estimate. Cornfield’s approach [45] was used to calculate the variance inflation factor. The betweenworksite variance was estimated to be 0.033 and the inflation factor 26.49. A difference of 23% could be de-
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tected with power greater than 0.9, a 4 0.05, two-sided test. Fat and fiber outcomes. The between-worksite variance for total fiber was estimated to be 3.72 and the total variance 60.95. For both fiber and fat, the inflation factor, the ratio of the between-worksite variance to the total variance, was estimated from the earlier (pretrial) screening data. Given the sample size, a mean increase in total fiber of 5 g could be detected with power greater than 0.9, a 4 0.05, two-sided test. The between-worksite variance for total fat was estimated to be 124.8 and the total variance 1,308.8. Given the sample size, a mean decrease in total fat of 9 g could be detected with power greater than 0.9, a 4 0.05, two-sided test. Total fat was used to estimate power because preliminary data on percentage of calories from fat were not available. Final sample size. The study sample size was 28 worksites including a total of 5,042 employees at baseline. The planned analyses using more complex models than those proposed by Donner et al. [44] should increase the power to detect differences with this sample size. Statistical Analysis Analysis approach. Standard errors given in this report and the comparison of characteristics of survey respondents and nonrespondents and intervention and control groups are computed taking the worksite clustering into account [46]. Generalized estimating equations [47] were used to take the correlations within worksite into account when adjusting for covariates in comparing responders and nonresponders. Intention to treat. In general, randomized clinical trials follow the accepted principle that participants should be analyzed in the treatment group to which they are assigned, regardless of postrandomization occurrences [48,49]. In a trial where the unit of analysis is the worksite and where there is in-and-out migration of workers and between-site transfers, application of the intention-to-treat principle is not straightforward. For this trial, participants in the primary analyses: (1) satisfy eligibility requirements to receive the survey mailing in the year being analyzed (worked in the pattern- and model-making area and were currently actively employed, retired, or on layoff) and (2) are assigned to the worksite they were associated with when they entered the trial. For analyses of screening compliance, an employee with missing data will be considered a noncomplier. Primary analyses of fat and fiber intake will be restricted to those completing a FFQ either at baseline or at 1 year. Missing values for those who completed the baseline FFQ but were nonrespondents to the survey
in the first year will be imputed using the first-year site mean for those of the same gender and retirement status. For those employees completing a FFQ in the first year, but missing a baseline FFQ, baseline nutrient intake values will be imputed from the baseline site mean for those of the same gender and retirement status . As an ancillary analysis of fiber and fat intake, analyses will be conducted without imputation, excluding those who do not have both a FFQ at baseline and Year 1. This approach is similar to that used in CATCH [50], where the clusters were elementary schools, with the exception that CATCH did not allow for migration into the site, as was necessary for this trial. RESULTS
The tables to follow describe the intervention and control groups’ baseline characteristics, compare respondents and nonrespondents to the baseline survey, and describe baseline survey findings for survey respondents. Table 1 gives employee characteristics by intervention and control worksites. The cohort is predominantly male and Caucasian. In contrast to other worksite programs, because both former and current TABLE 1 Comparison of Baseline Characteristics of Intervention and Control Worksites
Characteristic
Fifteen intervention worksites n 4 2,240
Thirteen control worksites n 4 2,802
P valuea
54 (0.70) 95 (1) 33 (2) 85 (2) 95 (1)
57 (0.75) 97 (1) 43 (3) 85 (1) 94 (1)
0.01 0.18 0.001 0.96 0.48
10 (1) 32 (2) 32 (2) 26 (2)
16 (2) 32 (1) 30 (1) 23 (2)
18 (1) 27 (0.11)
20 (1) 27 (0.11)
0.11 1.00
60 (4)
62 (2)
0.77
21 (2) 61 (3)
27 (1) 55 (2)
0.01 0.13
b
Demographics Age, mean (SEa), years Male, percent (SE) Retired, percent (SE) Married, percent (SE) Caucasian, percent (SE) Educationc (SE) <12 years 12 years 13–15 years ù16 years Lifestyle and health history Smoked cigarettes within 1 year of baseline,d percent (SE) Body mass index, mean (SE) Screened at least once in the 2 years prior to baseline (pretrial coverage) (SE) History of polyps of colorectal cancere (SE) Response to baseline survey
0.19
a Weighted means, standard errors and P values computed using ratio estimates to summarize across worksites adjusting for clustering within worksite. b 63 were missing ethnicity, 92 were missing years of education, and 33 were missing marital status. c Includes trade school. The statistical test was based on the continuous distribution of education. d 3,669 employees responded to the smoking question. Smoking information came from the baseline survey or from a health history questionnaire within a year of the baseline survey or from the 1-year survey. e From a physical examination report, pathology report, or employee selfreport.
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employees were eligible to participate, 39% (SE 4 2) were retired. Employees in the control worksites were older (P 4 0.01), more likely to be retired (P 4 0.001), and more likely to have a previous history of colorectal cancer or polyps (P 4 0.01) than employees in intervention worksites. There was no detectable difference in the proportion screened at least once in the 2 years prior to baseline (P 4 0.77). The overall response rate to the baseline survey was 58% (SE 4 2), ranging from 47 to 84% across the 28 worksites. No significant differences were found in crude response rates between the intervention and control worksites (Table 1). Table 2 gives the baseline demographic and healthrelated characteristics of respondents and nonrespondents to the baseline survey. Compared with nonrespondents, respondents were older and more likely to be Caucasian, male, married, retired, and better educated and less likely to be smokers (Table 2). They were more likely to have been screened in the preceding 2 years and also were more likely to have a personal history of colorectal cancer or polyps. Although body mass index was statistically significant, the difference in observed mean scores was minimal. Analyses by plant showed consistency across worksites in the com-
TABLE 2 Baseline Characteristics of Responders and Nonresponders to The Next Step Trial Baseline Survey FFQ or KAB survey
Characteristic Demographicsb Age, mean (SE) a years Male, percent (SE) Retired, percent (SE) Married, percent (SE) Caucasian, percent (SE) Education,c percent (SE) <12 years 12 years 13–15 years 16–18 years Lifestyle and health history Smoked cigarettes within 1 year of baselined percent (SE) Body mass index (SE) Screened at least once in the 2 years prior to baseline (pretrial coverage) (SE) History of polyps or colorectal cancer,e percent (SE) a
Responders (n 4 2,926)
Nonresponders (n 4 2,116)
P valuea
57 (0.59) 98 (0.2) 44 (2) 88 (1) 96 (1)
53 (0.84) 93 (1) 31 (2) 81 (2) 91 (1)
<0.001 <0.001 <0.001 <0.001 <0.001
10 (1) 31 (1) 30 (2) 28 (2)
17 (2) 33 (2) 31 (1) 20 (2)
18 (1) 27 (0.08)
23 (1) 27 (0.22)
<0.001 0.04
76 (2)
40 (3)
<0.001
30 (2)
17 (2)
<0.001
0.003
Weighted means, standard errors, and P values computed using ratio estimates to summarize across worksites adjusting for clustering within worksite. b 63 were missing ethnicity, 92 were missing years of education, and 33 were missing marital status. c Includes trade school. d 3,669 employees responded to the smoking question. Smoking information came from the baseline survey or from a health history questionnaire within a year of the baseline survey or from the 1-year survey. e From the physical examination report, pathology report, or patient report.
parisons of respondents and nonrespondents on these baseline characteristics. Table 3 gives baseline survey data for the total cohort of survey respondents by intervention and control worksites. No significant differences were found between intervention and control worksites for 9 of the 10 screening-related attitudinal scales from the KAB survey using P ø 0.10 as the critical level. Among survey responders, the intervention group was less likely to express belief in prevention of colorectal cancer. No significant differences were found between intervention and control worksites on the nutrition-related variables. Of survey respondents, 42% (SE 4 1) were in the action stage of change for adopting a low-fat diet, and 29% (SE 4 1) considered themselves to be maintaining a low-fat diet. Overall, respondents (28%, SE 4 1) were in the action stage of adopting a high-fiber diet, although more (37%, SE 4 1) considered themselves to be maintaining a high-fiber diet. In the total cohort, fat intake was relatively high (36.9% energy from fat, SE 4 0.2), and both fiber intake (8.8 g/1,000 kcal, SE 4 0.1) and fruit and vegetable intake (3.4 servings/day, SE 4 0.04) were moderate. Only 17% of respondents ate less than 30% energy from fat, 14% reported a diet with 12 or more grams of fiber/1,000 kcal, and 18% reported eating five or more servings of fruits and vegetables per day. DISCUSSION
The Next Step Trial was similar in design to recent worksite health promotion trials such as Working Well [11], Treatwell [12], and Five A Day [51] in that worksites, rather than individuals, were randomized to intervention or control groups. The Next Step Trial was different, however, in that it focused on colorectal cancer screening and targeted only employees at high risk for colorectal cancer. Employees in our study had been made aware of their increased risk through a newspaper article [19], the article by Tilley et al. [9], their union, and the plant medical staff who promoted the ongoing cancer screening program. Thus, this trial offers a special opportunity to evaluate a health and screening program in a group where the intervention can be linked to defined and recognized risk. The trial also is unique because it includes both active and retired employees and because it addresses both primary and secondary cancer prevention through a combination of interventions aimed at nutrition and screening. Because the screening intervention was added to an existing worksite screening program, the trial will assess the additive effect of a behavioral intervention on screening participation in an ongoing screening program. No structured cancer-related nutrition intervention was in place at the time the trial began; so, we will be able to test the impact of a de novo nutrition intervention.
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TABLE 3 Responders to The Next Step Trial Baseline Survey on Attitudes and Beliefs about Colorectal Cancer Screening and Nutrition Fifteen intervention worksites n 4 1,362
Thirteen control worksites n 4 1,541
P valueb
3.55 (0.02) 3.42 (0.04) 3.10 (0.03) 2.43 (0.03) 3.05 (0.03) 2.56 (0.03) 3.51 (0.02) 3.26 (0.02) 2.95 (0.03) 3.22 (0.03)
3.56 (0.02) 3.44 (0.02) 3.13 (0.03) 2.42 (0.03) 3.09 (0.02) 2.64 (0.05) 3.55 (0.02) 3.34 (0.02) 3.02 (0.04) 3.24 (0.03)
0.61 0.73 0.45 0.74 0.18 0.13 0.18 0.005 0.19 0.76
10 (0.4) 16 (1) 2 (0.3) 44 (1) 29 (1)
10 (0.4) 18 (1) 2 (0.3) 40 (1) 30 (1)
0.26
a
Screening attitudes and beliefs Salience and coherence, mean (SE)b Intention, mean (SE) Self-efficacy, mean (SE) Perceived susceptibility, mean (SE) Worries, mean (SE) Screening discomfort, mean (SE) Belief that colorectal cancer can be cured, mean (SE) Belief in prevention, mean (SE) Wants to do what family thinks about screening, mean (SE) Family thinks employee should be screened, mean (SE) Nutrition—stages of changea Fat consumption stages of change,d percentage of respondents • Precontemplation • Contemplation • Preparation • Action • Maintenance Fiber consumption stages of change,c percentage of repondents • Precomtemplation • Contemplation • Preparation • Action • Maintenance Nutrient intake (FFQ) Energy intake, mean (SE) Fat (percentage energy), mean (SE) Fiber (g/1,000 kcal), mean (SE) Servings of fruits per day,d n 4 2796, mean (SE) Servings of vegetables per day,d n 4 2794, mean (SE) Servings of fruits and vegetables per day,d n 4 2790, mean (SE)
7 (0.8) 25 (1) 4 (1) 28 (1) 37 (1) n 4 1,369 1,783 (22) 37.2 (0.3) 8.8 (0.1) 1.6 (0.04) 1.7 (0.04) 3.4 (0.05)
7 (0.3) 23 (1) 4 (0.4) 29 (1) 37 (1) n 4 1,541 1,735 (21) 36.7 (0.2) 8.9 (0.1) 1.6 (0.04) 1.7 (0.02) 3.4 (0.06)
0.66
0.11 0.23 0.75 0.79 0.73 0.72
a From KAB (survey on knowledge, attitudes and beliefs about screening and nutrition). For the screening variables, scale is 1–5 (strongly disagree to strongly agree). FFQ, food frequency questionnaire. n’s represent the number of employees responding to the survey. Nonrespondents are excluded. b Weighted means, standard errors, and P values computed using ratio estimates to summarize across worksites adjusting for clustering within worksite. c 97 employees responded with insufficient information to be staged for fat and 90 to be staged for fiber. d Fruits, sum of response to ‘‘how often did you eat fruit, not counting juices’’ and FFQ item on juices. Vegetables, sum of the response to ‘‘how often did you eat vegetables, not including salad or fried potatoes?’’ and two FFQ items on ‘‘green salad’’ and ‘‘potatoes, including boiled, baked, mashed and potato salad.’’ Fruits and vegetables, sum of two items. Missing data are determined by nonresponse and by a FFQ algorithm for errors. Statistical test was done on log transformation.
From the baseline analyses, we learned that pretrial coverage (screening at least once in the 2 years preceding baseline in 1993) was 61% in our study population prior to initiation of the enhanced screening intervention [9]. This figure is substantially higher than the 34% observed in a similar worksite program [52] offered over a 4-year interval. However, consistent with the sample size assumption, i.e., that participation would decrease over time, pretrial coverage in 1993 was less than the 79% coverage (screening at least once in first three cycles of the program) that we observed in our study population in 1989 [9]. These data on coverage suggest that while there is a decrease in participa-
tion over time, many in the cohort remained willing to participate in the screening program prior to the introduction of the behavioral intervention. The baseline survey response rate of 58% was similar to other studies using mailed food frequencies [53]. The Next Step Trial response rate was in line with the 61% response rate observed in the Working Well Trial in those worksites that administered the questionnaires by mail. In the Working Well Trial some worksites increased response rates by group administration of questionnaires during work time [11,54], an approach not possible in The Next Step Trial due to costs to the employer and the location of retirees off-site.
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Studies conducted at the worksite, particularly those relying on questionnaire data to measure study outcomes, would benefit from collecting data on-site. We found that respondents and nonrespondents to the FFQ and KAB baseline questionnaire differed significantly in terms of sociodemographic characteristics, medical history, and past screening behavior. The pattern of response was similar to that observed by Lerman and Shemer [55] who reported that respondents to health promotion programs tended to be people already committed to healthy life styles and by Lindsted et al. [56] who found that survey responders showed decreased mortality in the first few years after a survey. The intervention and control worksites differed in age, retirement status, and history of colorectal cancer and polyps. Although some of the intervention and control group differences were statistically significant, the magnitude of these differences was small. Given the large number of worksites, the large size of the total cohort, and the ability of the chosen statistical methods to adjust for covariates, we believe meaningful comparisons between the intervention and the control groups can be made. It is important to acknowledge that the generalizability of nutrition intervention results may be limited by respondent/nonrespondent differences because results will be based on survey data. However, given the randomized design, we concluded that comparison of intervention and control worksites would not be biased unless there was a differential response to the survey between intervention and control sites, a situation that did not occur. Our conclusion is consistent with that of Lindsted et al. [56]. In the Adventist health cohort study, their results suggested that, in general, for internal comparisons, no bias is likely to occur due to the healthy volunteer effect. The screening intervention is more likely to be generalizable to similar settings because compliance is measured both by survey data and by medical records. However, based on survey responses, control and intervention worksites did differ on one attitudinal measure related to screening effectiveness. Because we do not have survey data on all study participants, we will adjust for potential screening-related attitudinal differences between intervention and control worksites in primary analyses by controlling for recent screening behavior, a variable that is available on all employees and that indicates a predisposition toward preventive health behaviors. In conclusion, data from this trial will support a rigorous test of whether this high-risk employee population is responsive to targeted health promotion, early cancer detection, and prevention interventions. We believe that these data will be useful in planning health promotion programs for other high-risk groups.
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