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The knowledge and use of screening tests for colorectal and prostate cancer: Data from the 1987 national health interview survey
PREVENTIVE
MEDICINE
19, 562-574 (1990)
The Knowledge and Use of Screening Tests for Colorectal Prostate Cancer: Data from the 1987 National Health Interview Survey
and
MARTIN L. BROWN,PH.D., *,l ARNOLD L. POTOSKY,M.H.S.,” GREY B. THOMPSON,PH.D. ,t AND LARRY G. KESSLER,Sc.D.* *Applied Research Branch, Division of Cancer Prevention and Control, National Bethesda, Maryland 20892; and fDivision of Vital Statistics, National for Health Statistics, Hyattsville, Maryland 20782
Cancer Institute, Center
Data based on the 1987National Health Interview Survey are presented depicting factors associated with the knowledge and use of three tests for the early detection of colorectal and prostate cancer: digital rectal examination, fecal occult blood tests, and flexible sigmoidoscopy. The percentage of the at risk adult population who have ever heard of or had these tests is reported. The association of demographic, personal resource, and health system factors with knowledge of these tests is explored using multivariate logistic regression. Health system factors are most consistently associated with use of the tests and with knowledge. Family income, family size, education, knowledge of cancer early warning signs, and measures of encounters with the health care system are associated both with knowledge of and, independent of knowledge, with use of the tests. Residency in the non-South, being white or female, and having an optimistic attitude about cancer prevention are all factors associated with greater knowledge of the tests, but not greater use among those aware of the tests. Membership in a health maintenance organization is more strongly associated with knowledge and use of fecal occult blood tests than the other tests. No association was found between current smoking status and knowledge of or use of any of the tests. 6 IWO Academic Press, Inc.
INTRODUCTION
Colorectal and prostate cancer are major causes of morbidity and mortality in the United States. In 1990 there will be an estimated 155,000 new cases of colorectal cancer and 106,000 cases of prostate cancer. About 60,900 people will die from colorectal cancer and 30,000 will die from prostate cancer in 1990 (1). Several early detection techniques have the potential to improve survival prospects for these cancers. These techniques are the digital rectal examination (DRE), the fecal occult blood test (FOBT), and proctoscopy (rigid procto-sigmoidoscopy or flexible sigmoidoscopy). The first is used for the detection of colorectal (colon and rectal) cancer and prostate cancer, and the latter two are used to detect colon and rectal cancer (2, 3). Definitive evidence that these tests, when used routinely in asymptomatic populations, reduce mortality from colorectal and prostate cancer has yet to be presented, although several studies designed to clarify this question for FOBT and proctoscopy are currently under way or planned (47). On the basis of evidence of a survival benefit, and other considerations, a variety of professional organizations recommend the use of these tests, and use for specific high risk groups is ’
To
whom reprint requests should be addressed. 562
0091-7435/90$3.00 Copyright 0 1990 by Academic Press, Inc. AU rights of reproduction in any form reserved.
KNOWLEDGE
AND USE OF SCREENING TESTS
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almost universally endorsed (see Tables 1 and 2). This article presents data from the 1987National Health Interview Survey (NHIS) on the levels of knowledge and utilization of these techniques. This article also explores the association between various sociodemographic factors and knowledge and use of the tests under consideration. This information provides a useful background for subsequent studies designed to increase use in specific situations, now and in the future, where the tests are thought to be particularly appropriate. By investigating factors associated with both knowledge and use of cancer screening tests, this article also contributes to our general understanding of the decision-making process involved in the use of screening services. Screening Recommendations and Guidelines To date, the recommendations and guidelines of professional organizations regarding the advisability of routinely utilizing these techniques to screen for early cancer in asymptomatic patients have been mixed. Recommendations from several scientific and professional organizations are summarized in Tables 1 and 2. Past Research on Levels of Screening and Determinants of Utilization Table 3 summarizes the findings of past studies on the use of these cancer early detection tests. Rand Health Insurance Experiment (HZ@: In the HIE, a randomized trial of cost sharing on the demand for health services which ran from 1974 to 1982, less than 1% of those enrolled continuously over the first 3-year period (1974-1976) had a endoscopic examination. This number is increased to 3% if proctoscopic examinations categorized as nonpreventive are included (15). ACS surveys: The American Cancer Society has commissioned a number of TABLE 1 RECOMMENDATIONS/GUIDELINES
Source NC1 Working Guidelines (8)
ACS recommendations (9)
U.S. Preventive Services Task Force (IO, 11) American Gastroenterological Association/American Society for Gastrointestinal Endoscopy (12) Canadian Periodic Health Examination Task Force (13)
FOR EARLY DETECTION OF COLORECTAL CANCER
Recommendation/guideline Digital rectal examination as part of periodic health examinations Annual FOBT for age 350 Sigmoidoscopy every 3-5 years for age 250 Annual digital rectal examination for age 340 Annual FOBT for age 250 Sigmoidoscopy every 3-5 years after two negative exams performed 1 year apart, for age ~50 InsutXcient evidence either for or against fecal occult blood screening for age 945 Insufficient evidence either for or against periodic screening sigmoidoscopy in average risk persons age ~40 Digital rectal examination for age ~40 FOBT for age 850 Sigmoidoscopy for age 250 Insufficient evidence for or against FOBT or sigmoidoscopy in average risk individuals
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BROWN ET AL. TABLE 2 RECOMMENDATIONS/GUIDELINES FOR EARLY DETECTION OF PROSTATE CANCER
Recommendation/guideline
Source NC1 Working Guidelines (8)
Annual digital rectal examination for all men over 40 years of age Annual digital rectal examination for all men over 40 years of age Digital rectal examination not recommended for prostate cancer screening
ACS Recommendations (9) Canadian Periodic Health Examination Task Force (14)
surveys on the use of cancer screening services through the Gallup Organization. These data indicate that there was a substantial increase in the proportion of individuals receiving FOBT and proctoscopy between 1983 and 1987, while the prevalence of DREs remained roughly constant over that period. A more detailed ACS survey, done in 1982,found usage rates for proctoscopy similar to those in the Gallup survey, but somewhat higher rates for FOBT and DREs were found. This survey also found that 96% of those surveyed had heard of the digital rectal exam, 88% of the FOBT, and 75% of the proctoscopic exam. Of the respondents, 62% TABLE 3 UTILIZATION OF EARLY DETECTION TESTS (PROPORTION OF ADULTS WHO HAVE EVER HAD A TEST)
Test Digital rectal Men (age 40 + ) Women (age 40 +) All (age 40 + ) (within last 2 years) FOBT Men (age 50 + ) Women (age 50 + ) Men (age 40 + ) Women (age 40 + ) All (age 40 + ) (within last 2 years) All (age 20 + ) Proctoscopy Men (age 50+) Women (age 50+) Men (age 40 + ) Women (age 40 + ) All (age 40 + ) (within last 2 years) All (age 45-65) All (age 20 + )
1974-1976”
1976’
19806
1982’
54% 52%
1983’
1987b
56% 47%
53% 58%
29% 27%
43% 47% 38% 42%
32% 31%
43% 42% 38% 39%
70% 50% 17% 20%
44%
28% 13% 37% 35% 33% 20%
LIHealth Insurance Experiment (15). b ACS-Gallup Survey (16). ’ ACS-Shapiro Survey (9).
20%
KNOWLEDGE
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USE OF SCREENING
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believed that a digital rectal exam should be performed “when I’m feeling all right.” For FOBT and proctoscopy, 46 and 33%, respectively, believed the procedure should be done in that circumstance. Forty percent of the respondents had heard about colorectal cancer from either print or broadcast media, but only 35% had been advised by a physician to have a FOBT or proctoscopic examination (9, 16). In a survey of residents of a Southern California retirement community, Chao et al. found results similar to those of the ACS studies for FOBT (17). In summary, available data indicate that approximately one-half of adults over the age of 40 years have ever had a DRE, and this level of utilization has not changed significantly since 1980. Utilization rates for FOBT and proctoscopy appear to have increased somewhat during the 1980s although these tests are still less prevalent than the digital rectal exam. None of these earlier studies, however, utilized sufficient sample sizes to allow for the investigation of factors that are statistically associated with knowledge or use of these tests. In this regard the 1987 NHIS is unique. MATERIALS
AND METHODS
The Cancer Control Supplement to the 1987 National Health Interview Survey is designed to provide nationally generalizable information on knowledge of and barriers to the use of cancer screening techniques. It is also designed to provide detailed data on the determinants of screening, especially with regard to patient characteristics. The NHIS is a personal interview household survey using a nationwide sample of the civilian, noninstitutionalized population of the United States. For the Cancer Control Supplement of the survey, a sample adult (age ~18 years) was randomly selected from each family. Sample weights are assigned which reflect the probabilities of selection as well as adjustments for nonresponse and poststratification. The number of households responding to the Cancer Control Supplement of the 1987 NHIS is 22,043. Black and Hispanic households were oversampled. Limiting our multivariate regression analysis to those age 40 years and over reduced the unweighted sample size to about 9,000, and elimination of individuals because of missing values of dependent variables further reduced the sample size (see Table 5). The NHIS questionnaire includes questions about whether the respondent has ever heard of or has ever had various cancer screening tests. The digital rectal examination is described, by NHIS, as “when a finger is inserted in the rectum to check for problems.” The FOBT is described as “when the stool is examined to determine whether it contains blood.” The NHIS questionnaire describes a proctoscopic examination as “when a tube is inserted in the rectum to check for problems.” “Proctoscopy,” as used in the NHIS, is a generic term that is intended to include rigid procto-sigmoidoscopy as well as flexible fiber-optic sigmoidoscopy. No attempt was made, in the NHIS, to validate these questions. They were, however, carefully worded to be very specifically descriptive of the tests. Given the relatively invasive nature of the tests, it is likely that only a few people would ever forget having had them. There is probably considerable recall bias with regard to the exact date of having the tests, but data on test recency were not used in this article.
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ET AL.
Three basic outcomes are explored in this article. The first concerns knowledge about a particular screening technique. This outcome is measured by NHIS as an answer to the question “Have you ever heard of [the test]?” which is asked after a short description of the test is given. The second, which we call “conditional use,” concerns whether, having knowledge of the test, the person has actually received the screening service. NHIS asks a person whether the individual ever had the test and, if so, how recently. We use the answer to the “ever had” question from among those respondents who have answered affirmatively to the “ever heard” question to obtain a measure of conditional use. Having a cancer screening test, then, is viewed as the consequence of a two-step, sequential process. The individual must first gain knowledge of the test; once knowledge is obtained, the person may or may not decide to have the test. Data from the NHIS make it possible to examine the effect of various factors on each step of this process. The third outcome, which we call the “observed use” of the test, is measured by the proportion of the total sample who answer affirmatively to the “ever had” question. By comparing this outcome to the first two, it is possible to discern how the total impact of a factor may be decomposed between having knowledge of the test and using the test given knowledge. Observed use is also the proportion that is of ultimate interest for policy purposes. The factors studied in the NHIS that have been shown to be related to preventive medical care utilization in other studies (lg-21) are grouped into three categories: demographic, personal resources, and health system factors. Demographic factors-age, sex, race, region of residence, health status-are factors over which the individual has little or no immediate control, but which may be relevant to awareness or behavior with regard to the screening test. Personal resource factors are monetary, intellectual, and attitudinal characteristics which may enable an individual to assimilate information about early detection tests and to act on the basis of that information. These include family income, years of education, marital status, family size, optimism or pessimism about preventing cancer, knowledge of cancer early warning signs, and whether the person is currently a smoker. Health system factors refer to the frequency and nature of encounters with the health care system-whether a person has a usual source of care, whether a person is a member of a health maintenance organization (HMO), and time since the individual’s most recent doctor’s visit. Multivariate analysis was used to explore the association between the factors and the outcomes described above. Since the outcome variables are dichotomous, logistic regression was used. In addition, to take account of the complex sample design of the NHIS, the covariance matrix had to be adjusted. This was done using a software package, RTILOGIT, designed especially for this purpose (22). p coefficients from the logistic regression output were converted to odds ratio (OR) and corresponding 95% confidence intervals (CI) using standard procedures (23). For continuous variables, such as age and education, the odds ratio is interpreted as the percentage increase in the outcome per additional year of age or education. Age was entered as a continuous variable. Given the fact that the test could have taken place any time during several years prior to the survey, it is unlikely that interval effects (e.g., age ~65 vs >65 years) could be accurately
KNOWLEDGE
AND USE OF SCREENING TESTS
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portrayed. The regressions were run with education specified both as a continuous variable and as a discrete variable to test for graduation effects (e.g., 4 years of high school vs graduated from high school) and other discontinuities. Since the results of these two approaches were essentially identical, education is presented as a continuous variable for conciseness. Income was entered as a discrete variable because this reduced the number of missing values substantially, since more respondents were willing to answer the question that elicited income over relatively broad intervals. Family size was entered as a discrete variable based on the idea that what really matters is whether an adult has responsibility for dependent household members or not (roughly measured by household size of three or more). This notion was confirmed when alternative specifications of family size were tested. RESULTS
Levels of Knowledge and Utilization Table 4 shows results from the 1987 NHIS survey on overall levels of knowledge and utilization of the three tests under discussion. The first column in Table 4 denotes the proportion of the sample who answered “yes” to the question: “Have you ever heard of’ the respective test. The second column is the proportion of all respondents who “Have ever had” the test for any reason. While approximately 80% of the respondents have heard of the DRE and FOBT, only about 60% have heard of proctoscopy. While 60% have ever had a DRE, less than 40% have ever had a FOBT, and less than 25% have ever had a proctoscopic exam. The third column in Table 4 is the percentage of respondents who reported having the most recent respective test for a “health problem.” These instances should not be considered “screening” usage of the test since screening is usually considered to be use of an early detection examination in asymptomatic populations. The fourth column shows the residual of the third and second. This can be TABLE 4 RESULTSOF THE 1987 NHIS SURVEY”
Digital rectal exam Men Women FOBT Men Women Proctoscopy Men Women
(-4) Have heard
(B) Have had
(C) Health problem
03 03) - (Cl
0% Meet guidelinesb
77.2% 79.9%
58.0% 56.9%
10.9% 7.0%
47.1% 49.9%
18.9% 22.7%
80.9% 85.0%
36.2% 36.3%
5.9% 6.1%
30.3% 30.2%
16.9% 20.3
66.3% 87.7%
22.5% 20.2%
5.1% 4.8%
17.0% 15.4%
13.5% 11.1%
u For all persons age ~40 years. b Had exam within past year for DRE and FOBT; past 3 years for proctoscopy. For DRE, all persons age 240 years; for FOBT and proctoscopy, all persons age a50 years.
568
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ET AL.
read as a lower-bound estimate of the level of screening use of the tests, because the question asks only about the most recent instance of the tests. A person who has had the most recent test for a health problem may have had earlier tests as part of a routine or screening exam; that is, the “true” usage rate of these tests for screening is somewhere in between the levels given by columns C and D in Table 4. By this measure, about one-half of the population has ever had a DRE screening test, about one-third has ever had a FOBT screening test, and about one-fifth has ever had a screening proctoscopy. The fifth column of Table 4 shows the percentage of respondents who met the published guidelines for these tests, that is, to have a DRE and FOBT annually and proctoscopy every 3 years. For purposes of calculating this column, we did not differentiate between screening and nonscreening uses of the tests. These numbers contain an upward bias because they reflect answers to the question “How long ago did you have your most recent test?” not “How often do you have this test?” Factors Associated with Knowledge and Utilization The results of the multivariate logistic regressions are shown in Table 5. The columns in Table 5 correspond to the three outcomes described above. The column label Use/knowledge denotes conditional use, and the column label Use denotes observed use. The entries in Table 5 show estimated values for the odds ratio and the corresponding 95% confidence intervals for each factor. Entries in boldface type indicate that the confidence interval spans an interval that does not include the value of 1; that is, the odds ratio is statistically significantly different from 1. Socioeconomic factors. Several of the personal resource factors are consistently related to both knowledge and use of the tests. Family income is strongly related to knowledge, conditional use, and observed use for proctoscopy, the most expensive of the three tests. Family income over $40,000 is significantly associated with knowledge and use (conditional and observed) for DRE. For FOBT, income is associated with use, but not knowledge. Having a family size of three or more, essentially having children to care for (requiring expenditures of both income and time), is negatively related to all outcomes. Years of education is also positively related to both knowledge and use of the tests. When education was entered as a discrete variable (results not shown), graduation from high school vs attending high school was associated with increased levels of knowledge of DRE and proctoscopy. Knowledge of cancer early warning signs is positively related to all outcomes. In contrast, expressed optimism about cancer prevention is significantly and positively associated with knowledge and observed use of all three tests, but with conditional use only for DRE. Being married and living with spouse is also positively related to knowledge of FOBT and DRE, but not to conditional or observed use. Region. Living in a region of the country other than the South is positively related to knowledge of all three tests (although the coefficient for the West is positive, but not statistically significant). The results for conditional use are not
TABLE 5 ASSOCIATIONS BETWEEN FACTORS AND OUTCOMES 8,840 Knowledge
Test: digital rectal exam 7,226 Use/knowledge
8,762 Use
Factor
OR [95% CI]
OR [95% CI]
OR [95% CI]
Age” Sexb Race’ White Hispanic Regiond NE MW Income’ $20-39999 ~$40,000 Educatiod Marriedg Family size ~3~ Optimism’ Optimistic Pessimistic Knowledge’ Current smoker Health stat& Very good/excellent Fair/poor Had cancer Last MD visit’ Usual care HMO membership
1.00 ro.99, 1.001 1.12 (0.97, 1.291
1.01 [LOO, 1.021 0.72 [OH, 0.811
1.01 [l.oO, 1.011 0.84 [0.76, 0.941
1.43 H.15, 1.791 1.24 [0.91, 1.681
0.90 [0.70, 1.171 0.55 [0.39, 0.781
1.16 [0.95, 1.401 0.77 [0.59, 1.011
1.72 H.41, 2.101 1.30 [1.02, 1.651
0.91 [0.75, 1.111 0.94 [0.77, 1.141
1.19 [LOO, 1.421 1.09 [0.91, 1.301
1.05 1.30 1.11 1.19 0.78
[0.89, [l.Ol, [1.08, [0.95, [0.65,
1.221 1.691 1.141 1.491 0.941
1.05 1.31 1.02 1.06 0.71
[0.89, [1.06, [LOO, [0.86, [0.62,
1.241 1.631 1.051 1.301 0.821
1.06 1.32 1.07 1.14 0.71
[0.93, [1.09, [1.04, [0.95, [0.63,
1.201 MO] 1.09] 1.361 0.811
1.68 1.21 1.51 0.84
[1.38, [0.98, [1.30, [0.71,
2.051 I.491 1.751 1.Ol]
1.24 1.16 1.25 1.10
[l.OO. [0.92, [l.ll, [0.95,
1.541 1.451 1.401 1.271
1.48 1.21 1.40 0.98
[1.26, [1.02, [1.27, [0.86,
1.741 1.441 1.551 1.111
0.97 1.25 1.76 1.31 1.42 0.88
[0.84, [1.03, [1.36, [Lll, [1.16, [0.58,
1.121 1.511 2.281 1.551 1.721 1.351
0.91 1.31 1.44 1.99 1.54 1.35
[0.77, [1.08, [1.16, [1.67, [1.26, 10.99,
1.081 1.591 1.791 2.381 1.881 1.831
0.91 1.29 1.63 1.83 1.58 1.15
[0.80, [l.ll, [1.38, [1.56, [1.33, [0.90,
1.041 1.501 1.931 2.131 1.861 1.461
Unweighted
Unweighted
N:
Factor Age” Sexb Race’ White Hispanic Regiond NE MW IncomeP $20-39999 S$40,000 Education’ Married* Family size ~3~ Optimism’ Optimistic Pessimistic Knowledge’ Current smoker Health statu# Very good/excellent Fair/poor
N:
8,837 Knowledge
Test: fecal occult blood test 7,470 Use/knowledge
OR [95% CI]
OR [95% Cl]
OR [95% CI]
0.99 [0.99, I.001 1.43 [1.19, 1.721
1.02 [l.Ol, 1.031 0.85 [0.75, 0.951
1.02 [l.Ol, 1.021 0.93 [0.84, 1.041
1.77 [l&l, 2.241 0.65 [O&i, 0.921
0.82 [0.67, OSJ] 0.96 [0.67, 1.381
0.97 [0.81, 1.161 0.82 rO.59, 1.151
1.67 [1.32, 2.121 1.39 [1.08, 1.791
1.16 [0.99, 1.361 0.94 10.81, 1.091
1.26 [LOS, 1.481 1.01 [0.88, 1.161
1.11 1.23 1.15 1.39 0.77
[0.92, [0.92, [1.12, [1.05, [0.62,
1.341 1.631 1.181 1.831 0.951
1.16 1.39 1.06 1.06 0.71
[l.OO, [1.15, [1.03, rO.87, [0.61,
1.331 1.681 1.081 1.301 0.821
1.17 1.35 1.09 1.17 0.69
[1.02, [1.12, [1.07, IO.98, [0.61,
1.351 1.621 1.111 1.411 0.791
1.77 1.21 1.42 0.90
[l&I, [0.99, [1.19, [0.74,
2.181 1.491 1.701 1.111
1.12 1.00 1.13 1.19
[0.92, rO.82, [l.Ol, [1.03,
1.351 1.211 1.271 1.361
1.28 1.10 1.19 1.14
[l&S, [0.92, [1.07, [0.99,
1.551 1.321 1.331 1.301
1.01 [0.83, 1.221 0.84 rO.69, 1.031
0.87 [0.77, 0.981 1.39 [1.18, 1.641
8,664 Use
0.86 [0.76, 0.961 1.26 [1.08, 1.46)
TABLE
Unweighted N: Factor Had cancer Last MD visit’ Usual care HMO membership
5-Continued
8,837 Knowledge
Test: fecal occult blood test 7,470 Use/knowledge
8,664 Use
OR [95% CI]
OR [95% CI]
OR [95% CI]
1.12 [O&l, 1.501 1.54 H.22, 1.941 1.30 [1.06, 1.611 1.70 [1.07, 2.721
1.50 [1.27, 1.771 2.35 H.98, 2.781 1.40 [1.17, 1.68) 1.37 [1.02, 1.831
1.48 [1.25, 1.741
2.38 [2.03, 2.801 1.44 [1.21, 1.711 1.46 [1.08, 1.981
8,790 Knowledge
Test: proctoscopy 6,027 Use/knowledge
8,726 Use
Factor
OR [95% CI]
OR [95% CI]
OR [95% CI]
Agea Sexb Race’ White Hispanic Regiond NE MW Income’ $20-39999 e4o,ooo Education’ Married8 Family size 33” Optimism’ Optimistic Pessimistic Knowledge’ Current smoker Health stat& Very good/excellent Fair/poor Had cancer Last MD visit’ Usual care HMO membership
1.00 ro.99, 1.011 1.22 [l.M, 1.381
1.03 [1.03, 1.041
0.74 (0.64, 0.851
1.03 [1.02, 1.03) 0.81 [0.71, 0.921
0.87 [0.62, 1.221
1.06 [O&t, 1.331 1.14 [0.77, 1.681
1.34 [1.07, 1.671 1.08 [0.72, 1.641
1.18 [l.Ol, 1.371 1.41 [1.16, 1.701
0.93 [0.79, 1.101 1.09 [0.93, 1.281
1.02 [0.86, 1.201 1.22 [1.04, 1.431
1.27 1.77 1.15 1.56
1.27 D.07, 1.491 1.49 [1.21, 1.841 1.04 [l.Ol, 1.071 0.97 [0.76, 1.241 0.74 (0.63, 0.861
1.36 H.16, 1.60) 1.63 [1.32, 2.011 1.09 [1.06, 1.121 1.21 [O.%, 1.521 0.71 [0.61, 0.821
0.94 [0.84, 1.051
0.98 [0.77, 1.251 1.00 [0.76, 1.301 1.15 [l.OO, 1.321 1.05 [0.89, 1.241
1.34 [l.ll, 1.28 H.03, 1.36 [1.20, 1.01 [O&j,
1.07 [0.93, 1.221 1.02 fO.87, 1.191 1.63 [1.33, 2.00] 1.30 [1.09, 1.55] 1.35 [l.ll, 1.631
0.75 [O&l, 0.881 1.52 H.24, 1.861 1.35 [1.12, 1.631 1.83 (1.48, 2.251 1.45 [l.lS, 1.851
0.77 [Ohs, 0.89] 1.38 [1.16, 1.651
1.01 [0.78, 1.301
1.00 [0.66, 1.521
1.OO[0.67, 1.481
Unweighted N:
1.50 [1.24, 1.811
[l.ll, [1.47, [1.12, [1.30,
1.441 2.131 1.181 1.871
0.83 [0.72, 0.971 1.96 [1.65, 2.321 1.56 [1.31, 1.861 1.60 [l/N, 1.831
1.621 1.581 1.551 1.171
1.55 [1.31, 1.83) 1.92 [1.57, 2.361 1.53 [1.22, 1.90]
a All persons over age 40 years included in analysis; continuous variable. b Male is reference category. c Race categories are black, white, and hispanic; reference category is black. d Region categories are South, Northeast, Midwest, and West; reference category is South; no coefficients for West were significant. c Income categories are <$20,000; $20,000-39,999; ~$40,000; reference category is <$2O,ooO. f Years of school completed; continuous variable. 8 Married and living with spouse; reference category is all others. h Categories are 1 person, 2 persons , 33 persons; reference category is 2 persons; no coefficients for 1 person were significant. i Categories are optimism, pessimism, or no opinion about preventability of cancer; reference category is no opinion. i Knowledge of early warning signs for cancer; categories are bl and SO; reference cateogry is ~0. ’ Categories are fair and poor health, good health, and very good and excellent health; reference category is good health. ’ Categories are had medical visit within last 2 years, more than 2 years since last medical visit; reference category is more than 2 years.
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significant, however, and only for the Northeast for DRE and FOBT and the Midwest for proctoscopy is non-South residency associated with observed use. Race. Being white is positively related to knowledge of all three tests, but not to conditional use (conditional use for FOBT is negatively associated with being white). Only in the case of proctoscopy is being white positively associated with observed use. Hispanic ethnicity is negatively associated with knowledge and use in several instances. Gender. Women are more likely to have knowledge of FOBT and proctoscopy, but conditional use and observed use are higher for men for all three tests. Knowledge of the tests is unrelated to age, but conditional use and observed use are positively related to age for all tests. Healthfactors. Not surprisingly, those with relatively poor health status or with a history of cancer are more likely to have used all of the tests, while the results of knowledge are more mixed. There is no association between status as a current smoker and knowledge or use of the tests, except for a small positive effect in the case of conditional use for FOBT. Factors related to exposure to the health care system tend to be significant and large in effect. Having seen a doctor within the past 2 years (compared with >2 years) is strongly positively associated with all outcomes. Having a usual source of medical care is also strongly associated with all outcomes. Membership in a HMO is positively related to knowledge and use of FOBT. DISCUSSION
Levels of Knowledge and Utilization The study most comparable to the 1987 NHIS survey is the 1987 ACS-Gallup survey (16). The results of the NHIS are similar to those of the ACS-Gallup survey with regard to levels of awareness of the three tests discussed in this article. The ACSGallup survey, however, reported levels of awareness for FOBT that were somewhat lower than those found by NHIS (68% compared with 83%). As a comparison of Tables 3 and 4 shows, NHIS and ACS-Gallup are in fair agreement on usage rates for DRE and FOBT, but NHIS reports a smaller proportion ever having had a proctoscopic exam than ACS-Gallup (26% compared with 42%). This difference is much larger than can be explained by sampling variation. There are several differences between the two studies that may explain this discrepancy. NHIS interviews were conducted in person, whereas ACSGallup was a telephone survey. Proctoscopy was described as “when a tube is inserted in the rectum to check for problems,” in NHIS, while in AC&Gallup it is described as “an examination of the rectum and lower colon with an instrument for looking at the inside of the bowel to detect bowel cancer.” These wordings could have resulted in different reporting by respondents in the two surveys. The NHIS-reported rates of usage for proctoscopy within the past year of 5-9% are more consistent with Medicare utilization rates of about 5% (24) than are the ACS-Gallup-reported rates of about 20% for the same category. Factors Associated with Knowledge and Utilization In many instances, the association between factors and observed use appears to
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be explained by both levels of knowledge of the test and levels of use among those who are knowledgeable about the tests. The independent effect of knowledge can be seen most clearly in extreme cases where there is no association between the factor and conditional use. For example, a higher level of observed use of DRE is associated with residency in the Northeast (compared with the South), even though there is no association between residency in the Northeast and use of the test among those who have heard of it; but there is a strong association between Northeast residency and the proportion of people who have heard of the test. The independent contribution of knowledge to observed use is present for many of the factors, but is especially strong for region, optimism, awareness of early warning signs, and, to a lesser extent, the health system factors. This suggests that preventive health education may be an effective adjunct to increasing access to health care services for groups with low usage rates of screening tests. In agreement with other studies (18-20) the results of the 1987 NHIS indicate that low socioeconomic status is inversely associated with use of preventive medical care in the case of early detection for colorectal and prostate cancer. A few other results described above are notable, if not surprising. Not only is monetary income associated with the outcomes, but so is family size, which might be interpreted as a proxy for the (monetary, emotional, and time) burden of having family dependents. Another family variable, marital status, is associated with knowledge of the tests. This may indicate that marital status is a proxy for access to information about cancer tests through social networks. Marital status, however, is not related to observed use of the tests. The association of optimism about prevention and knowledge of cancer warning signs with knowledge of the tests, independent of general educational achievement, suggests that campaigns of public education focused specifically on cancer prevention may be effective. While we can only infer causal relationships from the cross-sectional data of the NHIS, this result also lends further credence to the recent conclusion of Berger and Leigh that education has a direct effect on health status, rather than being a proxy for some other unobserved variable (25). The mixed results for FOBT and proctoscopy for sex are notable. The coefftcient for observed use of these tests is higher for men than for women, even though the coefficient for knowledge is higher for women than for men. This is explained by the negative association between female gender and conditional use. One possible explanation for the finding that men tend to use these tests more than women is that men and women who have equivalent knowledge of the tests are being treated differently by their physicians. This would be a disturbing result since the incidence of colon cancer is not gender specific. The results for smoking status are interesting because it has been suggested that there is a “smoker’s personality” which is reflected in generally poor behavior toward health maintenance (26). Macrae et al. did find a negative relationship between smoking and compliance with the FOBT, but not with initial acceptance of the FOBT (21). That result, however, was based on a univariate analysis. We also found an association between smoking status and use of the tests in the univariate analysis. This apparent relationship did not carry over, however, into the multivariate analysis. Since smoking status is highly correlated with income
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and education, which are related to use of the tests, it is not surprising that the significance of the smoking factor disappeared in the multivariate regression. The measures of encounters with the health care system are associated with knowledge as well as with use for all tests. This suggests that the health care system serves as a source of information about early detection tests for cancer as well as a mechanism for delivering those tests. The FOBT is sensitive to HMO membership, while proctoscopy is not. This is consistent with the notion that HMOs tend to provide more preventive services than non-HMOs, but attempt to do so in a cost-effective way (proctoscopy is expensive compared with FOBT) (27). CONCLUSION
The NHIS shares the limitations common to all nonlongitudinal surveys. Therefore, the results presented here are not meant to be taken as conclusive evidence about the mechanisms that determine the use of screening tests. We do believe, however, that these data offer important clues for hypothesis formulation for investigators who wish to design specific intervention studies. These tests offer the potential to affect cancer morbidity and mortality; however, a consensus on whether these tests are efficacious for mass screening use in the general asymptomatic population has not yet been developed. There is more agreement that these tests should be given routinely to certain high risk groups. For these high risk groups, and as the evidence on the general efftcacy of these tests is clarified in the future, the results presented here should prove useful in designing programs to ensure that these tests are delivered at appropriate levels to eligible populations . ACKNOWLEDGMENTS The authors acknowledge Bill Helsel of Information Management Services for performing data processing and statistical calculations for this article. We thank Lisa Carter for typing the tables. The comments of Brenda Edwards, Ph.D., helped us greatly improve the presentation of data.
REFERENCES 1. Silverberg E, Boring CC, Squires TS. Cancer statistics, 1990. Ca 1990; 40~9-26. 2. Chodak GW. Routine screening for prostate cancer using the digital rectal examination. Prog Clin Biol Res 1988; 26987-95. 3. Winawer SJ. Screening for colorectal cancer. In: Devita VT, Hellman S, Rosenberg SA, Eds. Cancer, Principles and Practice of Oncology. Philadelphia: Lippincott, 1987. 4. Gilbertsen VA, McHugh RB, Schuman LM, ei al. Colon cancer control study: An interim report. In: Winawer S, Schottenfeld D, Sherlock P, Eds. Progress in Cancer Research and Treatment. Colorectal Cancer Prevention and Screening. New York: Raven Press, 1980: Vol. 13, 261-266. 5. Hardcastle JD, Farrands PA, Balfour TW, et al. Controlled trial of fecal occult blood testing in the detection of colorectal cancer. Lancer 1983; 2:ld. 6. Kewenter J, Bjork S, Haglind E, et al. Screening and rescreening for cola-rectal cancer. A controlled trial of fecal occult blood testing in 27,700 subjects. Cancer 1988; 62645451. 7. Byar D, Smart C, Prorok P. Prostate, Lung and Colorectal Cancer Screening Trial. Bethesda, MD: National Cancer Institute, 1989. 8. National Cancer Institute. Working Guidelines for Early Cancer Detection, Rationale and Supporting Evidence to Decrease Mortality. Bethesda, MD: National Cancer Institute, 1987.
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9. American Cancer Society. Cancer of the colon and rectum: Summary of a public attitude survey. CA 1983; 33:359-365. 10. Knight KK, Fielding JE, Battista RN. Occult blood screening for colorectal cancer. JAMA 1989; 261:587-593. 11. Selby JV, Friedman CD. U.S. Preventive services task force, recommendations for sigmoidoscopic screening. JAMA 1989; 261:594. 12. Fleischer DE, Goldberg SB, Browning TH, Cooper JN, Friedman E, Goldner FH, Keeffe EB, Smith LE. Detection and surveillance of colorectal cancer. JAMA 1989; 261:580-585. 13. Canadian Task Force on the Periodic Health Examination. The periodic health examination: 2. 1989update. Can Med Assoc J 1989; 141:209-216. 14. Canadian Task Force on the Periodic Health Examination. Can Med Assoc J 1979; 121:146. 15. Lurie N, Manning WC, Peterson C, er al. Preventive care: Do we practice what we preach? Am J Public Health 1987; 77:801-804. 16. Gallup Organization, Inc. The 1987 Survey of Public Awareness and Use of Cancer Detection Tests. Princeton: The Gallup Organization, Inc., 1988. 17. Chao A, Paganini A, Ross RK, Henderson BE. Use of preventive care by elderly. Prev Med 1987; 16~710-722. 18. Andersen R, Aday LA. Access to medical care in the U.S.: Realized and potential, Med Care 1978; 16533-546. 19. Burack RC, Liang J. The early detection of cancer in the primary-care setting: Factors associated with the acceptance and completion of recommended procedures. Prev Med 1987; 16~739-751. 20. Hayward RA, Shapiro MF, Freeman HE, Corey CR. Who gets screened for cervical and breast cancer. Arch Intern Med 1988; 14&l 177-1181. 21. Macrae FA, Hill DJ, et al. Predicting colon cancer screening behavior from health beliefs. Prev Med 1984; 13:115-126. 22. Shah BV, Folsom RE, Harrell FE, Dillard CN. Survey Data Analysis Software for Logistic Regression. Research Triangle Park, NC: Research Triangle Institute, 1984. 23. Hosmer DW, Lemeshow S. Applied Logistic Regression. New York: Wiley, 1989. 24. Mitchell JB, Wedig G, Cromwell J. Medicare physician fee freeze. Health Aff 1989; 821-33. 25. Berger MC, Leigh JP. Schooling, self-selection, and health. J Human Resources 1988; 14~433-455. 26. Fuchs VR. Time preference and health: An exploratory study. In: Fuch VR, Ed. Economic Aspects of Health. Chicago: Univ. of Chicago Press, 1982. 27. Luft HS. Why do HMOs seem to provide more health maintenance services? Milbank Memorial Fund Q 1978; 56140-168.
MEDICINE
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The Knowledge and Use of Screening Tests for Colorectal Prostate Cancer: Data from the 1987 National Health Interview Survey
and
MARTIN L. BROWN,PH.D., *,l ARNOLD L. POTOSKY,M.H.S.,” GREY B. THOMPSON,PH.D. ,t AND LARRY G. KESSLER,Sc.D.* *Applied Research Branch, Division of Cancer Prevention and Control, National Bethesda, Maryland 20892; and fDivision of Vital Statistics, National for Health Statistics, Hyattsville, Maryland 20782
Cancer Institute, Center
Data based on the 1987National Health Interview Survey are presented depicting factors associated with the knowledge and use of three tests for the early detection of colorectal and prostate cancer: digital rectal examination, fecal occult blood tests, and flexible sigmoidoscopy. The percentage of the at risk adult population who have ever heard of or had these tests is reported. The association of demographic, personal resource, and health system factors with knowledge of these tests is explored using multivariate logistic regression. Health system factors are most consistently associated with use of the tests and with knowledge. Family income, family size, education, knowledge of cancer early warning signs, and measures of encounters with the health care system are associated both with knowledge of and, independent of knowledge, with use of the tests. Residency in the non-South, being white or female, and having an optimistic attitude about cancer prevention are all factors associated with greater knowledge of the tests, but not greater use among those aware of the tests. Membership in a health maintenance organization is more strongly associated with knowledge and use of fecal occult blood tests than the other tests. No association was found between current smoking status and knowledge of or use of any of the tests. 6 IWO Academic Press, Inc.
INTRODUCTION
Colorectal and prostate cancer are major causes of morbidity and mortality in the United States. In 1990 there will be an estimated 155,000 new cases of colorectal cancer and 106,000 cases of prostate cancer. About 60,900 people will die from colorectal cancer and 30,000 will die from prostate cancer in 1990 (1). Several early detection techniques have the potential to improve survival prospects for these cancers. These techniques are the digital rectal examination (DRE), the fecal occult blood test (FOBT), and proctoscopy (rigid procto-sigmoidoscopy or flexible sigmoidoscopy). The first is used for the detection of colorectal (colon and rectal) cancer and prostate cancer, and the latter two are used to detect colon and rectal cancer (2, 3). Definitive evidence that these tests, when used routinely in asymptomatic populations, reduce mortality from colorectal and prostate cancer has yet to be presented, although several studies designed to clarify this question for FOBT and proctoscopy are currently under way or planned (47). On the basis of evidence of a survival benefit, and other considerations, a variety of professional organizations recommend the use of these tests, and use for specific high risk groups is ’
To
whom reprint requests should be addressed. 562
0091-7435/90$3.00 Copyright 0 1990 by Academic Press, Inc. AU rights of reproduction in any form reserved.
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almost universally endorsed (see Tables 1 and 2). This article presents data from the 1987National Health Interview Survey (NHIS) on the levels of knowledge and utilization of these techniques. This article also explores the association between various sociodemographic factors and knowledge and use of the tests under consideration. This information provides a useful background for subsequent studies designed to increase use in specific situations, now and in the future, where the tests are thought to be particularly appropriate. By investigating factors associated with both knowledge and use of cancer screening tests, this article also contributes to our general understanding of the decision-making process involved in the use of screening services. Screening Recommendations and Guidelines To date, the recommendations and guidelines of professional organizations regarding the advisability of routinely utilizing these techniques to screen for early cancer in asymptomatic patients have been mixed. Recommendations from several scientific and professional organizations are summarized in Tables 1 and 2. Past Research on Levels of Screening and Determinants of Utilization Table 3 summarizes the findings of past studies on the use of these cancer early detection tests. Rand Health Insurance Experiment (HZ@: In the HIE, a randomized trial of cost sharing on the demand for health services which ran from 1974 to 1982, less than 1% of those enrolled continuously over the first 3-year period (1974-1976) had a endoscopic examination. This number is increased to 3% if proctoscopic examinations categorized as nonpreventive are included (15). ACS surveys: The American Cancer Society has commissioned a number of TABLE 1 RECOMMENDATIONS/GUIDELINES
Source NC1 Working Guidelines (8)
ACS recommendations (9)
U.S. Preventive Services Task Force (IO, 11) American Gastroenterological Association/American Society for Gastrointestinal Endoscopy (12) Canadian Periodic Health Examination Task Force (13)
FOR EARLY DETECTION OF COLORECTAL CANCER
Recommendation/guideline Digital rectal examination as part of periodic health examinations Annual FOBT for age 350 Sigmoidoscopy every 3-5 years for age 250 Annual digital rectal examination for age 340 Annual FOBT for age 250 Sigmoidoscopy every 3-5 years after two negative exams performed 1 year apart, for age ~50 InsutXcient evidence either for or against fecal occult blood screening for age 945 Insufficient evidence either for or against periodic screening sigmoidoscopy in average risk persons age ~40 Digital rectal examination for age ~40 FOBT for age 850 Sigmoidoscopy for age 250 Insufficient evidence for or against FOBT or sigmoidoscopy in average risk individuals
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Recommendation/guideline
Source NC1 Working Guidelines (8)
Annual digital rectal examination for all men over 40 years of age Annual digital rectal examination for all men over 40 years of age Digital rectal examination not recommended for prostate cancer screening
ACS Recommendations (9) Canadian Periodic Health Examination Task Force (14)
surveys on the use of cancer screening services through the Gallup Organization. These data indicate that there was a substantial increase in the proportion of individuals receiving FOBT and proctoscopy between 1983 and 1987, while the prevalence of DREs remained roughly constant over that period. A more detailed ACS survey, done in 1982,found usage rates for proctoscopy similar to those in the Gallup survey, but somewhat higher rates for FOBT and DREs were found. This survey also found that 96% of those surveyed had heard of the digital rectal exam, 88% of the FOBT, and 75% of the proctoscopic exam. Of the respondents, 62% TABLE 3 UTILIZATION OF EARLY DETECTION TESTS (PROPORTION OF ADULTS WHO HAVE EVER HAD A TEST)
Test Digital rectal Men (age 40 + ) Women (age 40 +) All (age 40 + ) (within last 2 years) FOBT Men (age 50 + ) Women (age 50 + ) Men (age 40 + ) Women (age 40 + ) All (age 40 + ) (within last 2 years) All (age 20 + ) Proctoscopy Men (age 50+) Women (age 50+) Men (age 40 + ) Women (age 40 + ) All (age 40 + ) (within last 2 years) All (age 45-65) All (age 20 + )
1974-1976”
1976’
19806
1982’
54% 52%
1983’
1987b
56% 47%
53% 58%
29% 27%
43% 47% 38% 42%
32% 31%
43% 42% 38% 39%
70% 50% 17% 20%
44%
28% 13% 37% 35% 33% 20%
LIHealth Insurance Experiment (15). b ACS-Gallup Survey (16). ’ ACS-Shapiro Survey (9).
20%
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believed that a digital rectal exam should be performed “when I’m feeling all right.” For FOBT and proctoscopy, 46 and 33%, respectively, believed the procedure should be done in that circumstance. Forty percent of the respondents had heard about colorectal cancer from either print or broadcast media, but only 35% had been advised by a physician to have a FOBT or proctoscopic examination (9, 16). In a survey of residents of a Southern California retirement community, Chao et al. found results similar to those of the ACS studies for FOBT (17). In summary, available data indicate that approximately one-half of adults over the age of 40 years have ever had a DRE, and this level of utilization has not changed significantly since 1980. Utilization rates for FOBT and proctoscopy appear to have increased somewhat during the 1980s although these tests are still less prevalent than the digital rectal exam. None of these earlier studies, however, utilized sufficient sample sizes to allow for the investigation of factors that are statistically associated with knowledge or use of these tests. In this regard the 1987 NHIS is unique. MATERIALS
AND METHODS
The Cancer Control Supplement to the 1987 National Health Interview Survey is designed to provide nationally generalizable information on knowledge of and barriers to the use of cancer screening techniques. It is also designed to provide detailed data on the determinants of screening, especially with regard to patient characteristics. The NHIS is a personal interview household survey using a nationwide sample of the civilian, noninstitutionalized population of the United States. For the Cancer Control Supplement of the survey, a sample adult (age ~18 years) was randomly selected from each family. Sample weights are assigned which reflect the probabilities of selection as well as adjustments for nonresponse and poststratification. The number of households responding to the Cancer Control Supplement of the 1987 NHIS is 22,043. Black and Hispanic households were oversampled. Limiting our multivariate regression analysis to those age 40 years and over reduced the unweighted sample size to about 9,000, and elimination of individuals because of missing values of dependent variables further reduced the sample size (see Table 5). The NHIS questionnaire includes questions about whether the respondent has ever heard of or has ever had various cancer screening tests. The digital rectal examination is described, by NHIS, as “when a finger is inserted in the rectum to check for problems.” The FOBT is described as “when the stool is examined to determine whether it contains blood.” The NHIS questionnaire describes a proctoscopic examination as “when a tube is inserted in the rectum to check for problems.” “Proctoscopy,” as used in the NHIS, is a generic term that is intended to include rigid procto-sigmoidoscopy as well as flexible fiber-optic sigmoidoscopy. No attempt was made, in the NHIS, to validate these questions. They were, however, carefully worded to be very specifically descriptive of the tests. Given the relatively invasive nature of the tests, it is likely that only a few people would ever forget having had them. There is probably considerable recall bias with regard to the exact date of having the tests, but data on test recency were not used in this article.
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Three basic outcomes are explored in this article. The first concerns knowledge about a particular screening technique. This outcome is measured by NHIS as an answer to the question “Have you ever heard of [the test]?” which is asked after a short description of the test is given. The second, which we call “conditional use,” concerns whether, having knowledge of the test, the person has actually received the screening service. NHIS asks a person whether the individual ever had the test and, if so, how recently. We use the answer to the “ever had” question from among those respondents who have answered affirmatively to the “ever heard” question to obtain a measure of conditional use. Having a cancer screening test, then, is viewed as the consequence of a two-step, sequential process. The individual must first gain knowledge of the test; once knowledge is obtained, the person may or may not decide to have the test. Data from the NHIS make it possible to examine the effect of various factors on each step of this process. The third outcome, which we call the “observed use” of the test, is measured by the proportion of the total sample who answer affirmatively to the “ever had” question. By comparing this outcome to the first two, it is possible to discern how the total impact of a factor may be decomposed between having knowledge of the test and using the test given knowledge. Observed use is also the proportion that is of ultimate interest for policy purposes. The factors studied in the NHIS that have been shown to be related to preventive medical care utilization in other studies (lg-21) are grouped into three categories: demographic, personal resources, and health system factors. Demographic factors-age, sex, race, region of residence, health status-are factors over which the individual has little or no immediate control, but which may be relevant to awareness or behavior with regard to the screening test. Personal resource factors are monetary, intellectual, and attitudinal characteristics which may enable an individual to assimilate information about early detection tests and to act on the basis of that information. These include family income, years of education, marital status, family size, optimism or pessimism about preventing cancer, knowledge of cancer early warning signs, and whether the person is currently a smoker. Health system factors refer to the frequency and nature of encounters with the health care system-whether a person has a usual source of care, whether a person is a member of a health maintenance organization (HMO), and time since the individual’s most recent doctor’s visit. Multivariate analysis was used to explore the association between the factors and the outcomes described above. Since the outcome variables are dichotomous, logistic regression was used. In addition, to take account of the complex sample design of the NHIS, the covariance matrix had to be adjusted. This was done using a software package, RTILOGIT, designed especially for this purpose (22). p coefficients from the logistic regression output were converted to odds ratio (OR) and corresponding 95% confidence intervals (CI) using standard procedures (23). For continuous variables, such as age and education, the odds ratio is interpreted as the percentage increase in the outcome per additional year of age or education. Age was entered as a continuous variable. Given the fact that the test could have taken place any time during several years prior to the survey, it is unlikely that interval effects (e.g., age ~65 vs >65 years) could be accurately
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portrayed. The regressions were run with education specified both as a continuous variable and as a discrete variable to test for graduation effects (e.g., 4 years of high school vs graduated from high school) and other discontinuities. Since the results of these two approaches were essentially identical, education is presented as a continuous variable for conciseness. Income was entered as a discrete variable because this reduced the number of missing values substantially, since more respondents were willing to answer the question that elicited income over relatively broad intervals. Family size was entered as a discrete variable based on the idea that what really matters is whether an adult has responsibility for dependent household members or not (roughly measured by household size of three or more). This notion was confirmed when alternative specifications of family size were tested. RESULTS
Levels of Knowledge and Utilization Table 4 shows results from the 1987 NHIS survey on overall levels of knowledge and utilization of the three tests under discussion. The first column in Table 4 denotes the proportion of the sample who answered “yes” to the question: “Have you ever heard of’ the respective test. The second column is the proportion of all respondents who “Have ever had” the test for any reason. While approximately 80% of the respondents have heard of the DRE and FOBT, only about 60% have heard of proctoscopy. While 60% have ever had a DRE, less than 40% have ever had a FOBT, and less than 25% have ever had a proctoscopic exam. The third column in Table 4 is the percentage of respondents who reported having the most recent respective test for a “health problem.” These instances should not be considered “screening” usage of the test since screening is usually considered to be use of an early detection examination in asymptomatic populations. The fourth column shows the residual of the third and second. This can be TABLE 4 RESULTSOF THE 1987 NHIS SURVEY”
Digital rectal exam Men Women FOBT Men Women Proctoscopy Men Women
(-4) Have heard
(B) Have had
(C) Health problem
03 03) - (Cl
0% Meet guidelinesb
77.2% 79.9%
58.0% 56.9%
10.9% 7.0%
47.1% 49.9%
18.9% 22.7%
80.9% 85.0%
36.2% 36.3%
5.9% 6.1%
30.3% 30.2%
16.9% 20.3
66.3% 87.7%
22.5% 20.2%
5.1% 4.8%
17.0% 15.4%
13.5% 11.1%
u For all persons age ~40 years. b Had exam within past year for DRE and FOBT; past 3 years for proctoscopy. For DRE, all persons age 240 years; for FOBT and proctoscopy, all persons age a50 years.
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read as a lower-bound estimate of the level of screening use of the tests, because the question asks only about the most recent instance of the tests. A person who has had the most recent test for a health problem may have had earlier tests as part of a routine or screening exam; that is, the “true” usage rate of these tests for screening is somewhere in between the levels given by columns C and D in Table 4. By this measure, about one-half of the population has ever had a DRE screening test, about one-third has ever had a FOBT screening test, and about one-fifth has ever had a screening proctoscopy. The fifth column of Table 4 shows the percentage of respondents who met the published guidelines for these tests, that is, to have a DRE and FOBT annually and proctoscopy every 3 years. For purposes of calculating this column, we did not differentiate between screening and nonscreening uses of the tests. These numbers contain an upward bias because they reflect answers to the question “How long ago did you have your most recent test?” not “How often do you have this test?” Factors Associated with Knowledge and Utilization The results of the multivariate logistic regressions are shown in Table 5. The columns in Table 5 correspond to the three outcomes described above. The column label Use/knowledge denotes conditional use, and the column label Use denotes observed use. The entries in Table 5 show estimated values for the odds ratio and the corresponding 95% confidence intervals for each factor. Entries in boldface type indicate that the confidence interval spans an interval that does not include the value of 1; that is, the odds ratio is statistically significantly different from 1. Socioeconomic factors. Several of the personal resource factors are consistently related to both knowledge and use of the tests. Family income is strongly related to knowledge, conditional use, and observed use for proctoscopy, the most expensive of the three tests. Family income over $40,000 is significantly associated with knowledge and use (conditional and observed) for DRE. For FOBT, income is associated with use, but not knowledge. Having a family size of three or more, essentially having children to care for (requiring expenditures of both income and time), is negatively related to all outcomes. Years of education is also positively related to both knowledge and use of the tests. When education was entered as a discrete variable (results not shown), graduation from high school vs attending high school was associated with increased levels of knowledge of DRE and proctoscopy. Knowledge of cancer early warning signs is positively related to all outcomes. In contrast, expressed optimism about cancer prevention is significantly and positively associated with knowledge and observed use of all three tests, but with conditional use only for DRE. Being married and living with spouse is also positively related to knowledge of FOBT and DRE, but not to conditional or observed use. Region. Living in a region of the country other than the South is positively related to knowledge of all three tests (although the coefficient for the West is positive, but not statistically significant). The results for conditional use are not
TABLE 5 ASSOCIATIONS BETWEEN FACTORS AND OUTCOMES 8,840 Knowledge
Test: digital rectal exam 7,226 Use/knowledge
8,762 Use
Factor
OR [95% CI]
OR [95% CI]
OR [95% CI]
Age” Sexb Race’ White Hispanic Regiond NE MW Income’ $20-39999 ~$40,000 Educatiod Marriedg Family size ~3~ Optimism’ Optimistic Pessimistic Knowledge’ Current smoker Health stat& Very good/excellent Fair/poor Had cancer Last MD visit’ Usual care HMO membership
1.00 ro.99, 1.001 1.12 (0.97, 1.291
1.01 [LOO, 1.021 0.72 [OH, 0.811
1.01 [l.oO, 1.011 0.84 [0.76, 0.941
1.43 H.15, 1.791 1.24 [0.91, 1.681
0.90 [0.70, 1.171 0.55 [0.39, 0.781
1.16 [0.95, 1.401 0.77 [0.59, 1.011
1.72 H.41, 2.101 1.30 [1.02, 1.651
0.91 [0.75, 1.111 0.94 [0.77, 1.141
1.19 [LOO, 1.421 1.09 [0.91, 1.301
1.05 1.30 1.11 1.19 0.78
[0.89, [l.Ol, [1.08, [0.95, [0.65,
1.221 1.691 1.141 1.491 0.941
1.05 1.31 1.02 1.06 0.71
[0.89, [1.06, [LOO, [0.86, [0.62,
1.241 1.631 1.051 1.301 0.821
1.06 1.32 1.07 1.14 0.71
[0.93, [1.09, [1.04, [0.95, [0.63,
1.201 MO] 1.09] 1.361 0.811
1.68 1.21 1.51 0.84
[1.38, [0.98, [1.30, [0.71,
2.051 I.491 1.751 1.Ol]
1.24 1.16 1.25 1.10
[l.OO. [0.92, [l.ll, [0.95,
1.541 1.451 1.401 1.271
1.48 1.21 1.40 0.98
[1.26, [1.02, [1.27, [0.86,
1.741 1.441 1.551 1.111
0.97 1.25 1.76 1.31 1.42 0.88
[0.84, [1.03, [1.36, [Lll, [1.16, [0.58,
1.121 1.511 2.281 1.551 1.721 1.351
0.91 1.31 1.44 1.99 1.54 1.35
[0.77, [1.08, [1.16, [1.67, [1.26, 10.99,
1.081 1.591 1.791 2.381 1.881 1.831
0.91 1.29 1.63 1.83 1.58 1.15
[0.80, [l.ll, [1.38, [1.56, [1.33, [0.90,
1.041 1.501 1.931 2.131 1.861 1.461
Unweighted
Unweighted
N:
Factor Age” Sexb Race’ White Hispanic Regiond NE MW IncomeP $20-39999 S$40,000 Education’ Married* Family size ~3~ Optimism’ Optimistic Pessimistic Knowledge’ Current smoker Health statu# Very good/excellent Fair/poor
N:
8,837 Knowledge
Test: fecal occult blood test 7,470 Use/knowledge
OR [95% CI]
OR [95% Cl]
OR [95% CI]
0.99 [0.99, I.001 1.43 [1.19, 1.721
1.02 [l.Ol, 1.031 0.85 [0.75, 0.951
1.02 [l.Ol, 1.021 0.93 [0.84, 1.041
1.77 [l&l, 2.241 0.65 [O&i, 0.921
0.82 [0.67, OSJ] 0.96 [0.67, 1.381
0.97 [0.81, 1.161 0.82 rO.59, 1.151
1.67 [1.32, 2.121 1.39 [1.08, 1.791
1.16 [0.99, 1.361 0.94 10.81, 1.091
1.26 [LOS, 1.481 1.01 [0.88, 1.161
1.11 1.23 1.15 1.39 0.77
[0.92, [0.92, [1.12, [1.05, [0.62,
1.341 1.631 1.181 1.831 0.951
1.16 1.39 1.06 1.06 0.71
[l.OO, [1.15, [1.03, rO.87, [0.61,
1.331 1.681 1.081 1.301 0.821
1.17 1.35 1.09 1.17 0.69
[1.02, [1.12, [1.07, IO.98, [0.61,
1.351 1.621 1.111 1.411 0.791
1.77 1.21 1.42 0.90
[l&I, [0.99, [1.19, [0.74,
2.181 1.491 1.701 1.111
1.12 1.00 1.13 1.19
[0.92, rO.82, [l.Ol, [1.03,
1.351 1.211 1.271 1.361
1.28 1.10 1.19 1.14
[l&S, [0.92, [1.07, [0.99,
1.551 1.321 1.331 1.301
1.01 [0.83, 1.221 0.84 rO.69, 1.031
0.87 [0.77, 0.981 1.39 [1.18, 1.641
8,664 Use
0.86 [0.76, 0.961 1.26 [1.08, 1.46)
TABLE
Unweighted N: Factor Had cancer Last MD visit’ Usual care HMO membership
5-Continued
8,837 Knowledge
Test: fecal occult blood test 7,470 Use/knowledge
8,664 Use
OR [95% CI]
OR [95% CI]
OR [95% CI]
1.12 [O&l, 1.501 1.54 H.22, 1.941 1.30 [1.06, 1.611 1.70 [1.07, 2.721
1.50 [1.27, 1.771 2.35 H.98, 2.781 1.40 [1.17, 1.68) 1.37 [1.02, 1.831
1.48 [1.25, 1.741
2.38 [2.03, 2.801 1.44 [1.21, 1.711 1.46 [1.08, 1.981
8,790 Knowledge
Test: proctoscopy 6,027 Use/knowledge
8,726 Use
Factor
OR [95% CI]
OR [95% CI]
OR [95% CI]
Agea Sexb Race’ White Hispanic Regiond NE MW Income’ $20-39999 e4o,ooo Education’ Married8 Family size 33” Optimism’ Optimistic Pessimistic Knowledge’ Current smoker Health stat& Very good/excellent Fair/poor Had cancer Last MD visit’ Usual care HMO membership
1.00 ro.99, 1.011 1.22 [l.M, 1.381
1.03 [1.03, 1.041
0.74 (0.64, 0.851
1.03 [1.02, 1.03) 0.81 [0.71, 0.921
0.87 [0.62, 1.221
1.06 [O&t, 1.331 1.14 [0.77, 1.681
1.34 [1.07, 1.671 1.08 [0.72, 1.641
1.18 [l.Ol, 1.371 1.41 [1.16, 1.701
0.93 [0.79, 1.101 1.09 [0.93, 1.281
1.02 [0.86, 1.201 1.22 [1.04, 1.431
1.27 1.77 1.15 1.56
1.27 D.07, 1.491 1.49 [1.21, 1.841 1.04 [l.Ol, 1.071 0.97 [0.76, 1.241 0.74 (0.63, 0.861
1.36 H.16, 1.60) 1.63 [1.32, 2.011 1.09 [1.06, 1.121 1.21 [O.%, 1.521 0.71 [0.61, 0.821
0.94 [0.84, 1.051
0.98 [0.77, 1.251 1.00 [0.76, 1.301 1.15 [l.OO, 1.321 1.05 [0.89, 1.241
1.34 [l.ll, 1.28 H.03, 1.36 [1.20, 1.01 [O&j,
1.07 [0.93, 1.221 1.02 fO.87, 1.191 1.63 [1.33, 2.00] 1.30 [1.09, 1.55] 1.35 [l.ll, 1.631
0.75 [O&l, 0.881 1.52 H.24, 1.861 1.35 [1.12, 1.631 1.83 (1.48, 2.251 1.45 [l.lS, 1.851
0.77 [Ohs, 0.89] 1.38 [1.16, 1.651
1.01 [0.78, 1.301
1.00 [0.66, 1.521
1.OO[0.67, 1.481
Unweighted N:
1.50 [1.24, 1.811
[l.ll, [1.47, [1.12, [1.30,
1.441 2.131 1.181 1.871
0.83 [0.72, 0.971 1.96 [1.65, 2.321 1.56 [1.31, 1.861 1.60 [l/N, 1.831
1.621 1.581 1.551 1.171
1.55 [1.31, 1.83) 1.92 [1.57, 2.361 1.53 [1.22, 1.90]
a All persons over age 40 years included in analysis; continuous variable. b Male is reference category. c Race categories are black, white, and hispanic; reference category is black. d Region categories are South, Northeast, Midwest, and West; reference category is South; no coefficients for West were significant. c Income categories are <$20,000; $20,000-39,999; ~$40,000; reference category is <$2O,ooO. f Years of school completed; continuous variable. 8 Married and living with spouse; reference category is all others. h Categories are 1 person, 2 persons , 33 persons; reference category is 2 persons; no coefficients for 1 person were significant. i Categories are optimism, pessimism, or no opinion about preventability of cancer; reference category is no opinion. i Knowledge of early warning signs for cancer; categories are bl and SO; reference cateogry is ~0. ’ Categories are fair and poor health, good health, and very good and excellent health; reference category is good health. ’ Categories are had medical visit within last 2 years, more than 2 years since last medical visit; reference category is more than 2 years.
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significant, however, and only for the Northeast for DRE and FOBT and the Midwest for proctoscopy is non-South residency associated with observed use. Race. Being white is positively related to knowledge of all three tests, but not to conditional use (conditional use for FOBT is negatively associated with being white). Only in the case of proctoscopy is being white positively associated with observed use. Hispanic ethnicity is negatively associated with knowledge and use in several instances. Gender. Women are more likely to have knowledge of FOBT and proctoscopy, but conditional use and observed use are higher for men for all three tests. Knowledge of the tests is unrelated to age, but conditional use and observed use are positively related to age for all tests. Healthfactors. Not surprisingly, those with relatively poor health status or with a history of cancer are more likely to have used all of the tests, while the results of knowledge are more mixed. There is no association between status as a current smoker and knowledge or use of the tests, except for a small positive effect in the case of conditional use for FOBT. Factors related to exposure to the health care system tend to be significant and large in effect. Having seen a doctor within the past 2 years (compared with >2 years) is strongly positively associated with all outcomes. Having a usual source of medical care is also strongly associated with all outcomes. Membership in a HMO is positively related to knowledge and use of FOBT. DISCUSSION
Levels of Knowledge and Utilization The study most comparable to the 1987 NHIS survey is the 1987 ACS-Gallup survey (16). The results of the NHIS are similar to those of the ACS-Gallup survey with regard to levels of awareness of the three tests discussed in this article. The ACSGallup survey, however, reported levels of awareness for FOBT that were somewhat lower than those found by NHIS (68% compared with 83%). As a comparison of Tables 3 and 4 shows, NHIS and ACS-Gallup are in fair agreement on usage rates for DRE and FOBT, but NHIS reports a smaller proportion ever having had a proctoscopic exam than ACS-Gallup (26% compared with 42%). This difference is much larger than can be explained by sampling variation. There are several differences between the two studies that may explain this discrepancy. NHIS interviews were conducted in person, whereas ACSGallup was a telephone survey. Proctoscopy was described as “when a tube is inserted in the rectum to check for problems,” in NHIS, while in AC&Gallup it is described as “an examination of the rectum and lower colon with an instrument for looking at the inside of the bowel to detect bowel cancer.” These wordings could have resulted in different reporting by respondents in the two surveys. The NHIS-reported rates of usage for proctoscopy within the past year of 5-9% are more consistent with Medicare utilization rates of about 5% (24) than are the ACS-Gallup-reported rates of about 20% for the same category. Factors Associated with Knowledge and Utilization In many instances, the association between factors and observed use appears to
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be explained by both levels of knowledge of the test and levels of use among those who are knowledgeable about the tests. The independent effect of knowledge can be seen most clearly in extreme cases where there is no association between the factor and conditional use. For example, a higher level of observed use of DRE is associated with residency in the Northeast (compared with the South), even though there is no association between residency in the Northeast and use of the test among those who have heard of it; but there is a strong association between Northeast residency and the proportion of people who have heard of the test. The independent contribution of knowledge to observed use is present for many of the factors, but is especially strong for region, optimism, awareness of early warning signs, and, to a lesser extent, the health system factors. This suggests that preventive health education may be an effective adjunct to increasing access to health care services for groups with low usage rates of screening tests. In agreement with other studies (18-20) the results of the 1987 NHIS indicate that low socioeconomic status is inversely associated with use of preventive medical care in the case of early detection for colorectal and prostate cancer. A few other results described above are notable, if not surprising. Not only is monetary income associated with the outcomes, but so is family size, which might be interpreted as a proxy for the (monetary, emotional, and time) burden of having family dependents. Another family variable, marital status, is associated with knowledge of the tests. This may indicate that marital status is a proxy for access to information about cancer tests through social networks. Marital status, however, is not related to observed use of the tests. The association of optimism about prevention and knowledge of cancer warning signs with knowledge of the tests, independent of general educational achievement, suggests that campaigns of public education focused specifically on cancer prevention may be effective. While we can only infer causal relationships from the cross-sectional data of the NHIS, this result also lends further credence to the recent conclusion of Berger and Leigh that education has a direct effect on health status, rather than being a proxy for some other unobserved variable (25). The mixed results for FOBT and proctoscopy for sex are notable. The coefftcient for observed use of these tests is higher for men than for women, even though the coefficient for knowledge is higher for women than for men. This is explained by the negative association between female gender and conditional use. One possible explanation for the finding that men tend to use these tests more than women is that men and women who have equivalent knowledge of the tests are being treated differently by their physicians. This would be a disturbing result since the incidence of colon cancer is not gender specific. The results for smoking status are interesting because it has been suggested that there is a “smoker’s personality” which is reflected in generally poor behavior toward health maintenance (26). Macrae et al. did find a negative relationship between smoking and compliance with the FOBT, but not with initial acceptance of the FOBT (21). That result, however, was based on a univariate analysis. We also found an association between smoking status and use of the tests in the univariate analysis. This apparent relationship did not carry over, however, into the multivariate analysis. Since smoking status is highly correlated with income
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and education, which are related to use of the tests, it is not surprising that the significance of the smoking factor disappeared in the multivariate regression. The measures of encounters with the health care system are associated with knowledge as well as with use for all tests. This suggests that the health care system serves as a source of information about early detection tests for cancer as well as a mechanism for delivering those tests. The FOBT is sensitive to HMO membership, while proctoscopy is not. This is consistent with the notion that HMOs tend to provide more preventive services than non-HMOs, but attempt to do so in a cost-effective way (proctoscopy is expensive compared with FOBT) (27). CONCLUSION
The NHIS shares the limitations common to all nonlongitudinal surveys. Therefore, the results presented here are not meant to be taken as conclusive evidence about the mechanisms that determine the use of screening tests. We do believe, however, that these data offer important clues for hypothesis formulation for investigators who wish to design specific intervention studies. These tests offer the potential to affect cancer morbidity and mortality; however, a consensus on whether these tests are efficacious for mass screening use in the general asymptomatic population has not yet been developed. There is more agreement that these tests should be given routinely to certain high risk groups. For these high risk groups, and as the evidence on the general efftcacy of these tests is clarified in the future, the results presented here should prove useful in designing programs to ensure that these tests are delivered at appropriate levels to eligible populations . ACKNOWLEDGMENTS The authors acknowledge Bill Helsel of Information Management Services for performing data processing and statistical calculations for this article. We thank Lisa Carter for typing the tables. The comments of Brenda Edwards, Ph.D., helped us greatly improve the presentation of data.
REFERENCES 1. Silverberg E, Boring CC, Squires TS. Cancer statistics, 1990. Ca 1990; 40~9-26. 2. Chodak GW. Routine screening for prostate cancer using the digital rectal examination. Prog Clin Biol Res 1988; 26987-95. 3. Winawer SJ. Screening for colorectal cancer. In: Devita VT, Hellman S, Rosenberg SA, Eds. Cancer, Principles and Practice of Oncology. Philadelphia: Lippincott, 1987. 4. Gilbertsen VA, McHugh RB, Schuman LM, ei al. Colon cancer control study: An interim report. In: Winawer S, Schottenfeld D, Sherlock P, Eds. Progress in Cancer Research and Treatment. Colorectal Cancer Prevention and Screening. New York: Raven Press, 1980: Vol. 13, 261-266. 5. Hardcastle JD, Farrands PA, Balfour TW, et al. Controlled trial of fecal occult blood testing in the detection of colorectal cancer. Lancer 1983; 2:ld. 6. Kewenter J, Bjork S, Haglind E, et al. Screening and rescreening for cola-rectal cancer. A controlled trial of fecal occult blood testing in 27,700 subjects. Cancer 1988; 62645451. 7. Byar D, Smart C, Prorok P. Prostate, Lung and Colorectal Cancer Screening Trial. Bethesda, MD: National Cancer Institute, 1989. 8. National Cancer Institute. Working Guidelines for Early Cancer Detection, Rationale and Supporting Evidence to Decrease Mortality. Bethesda, MD: National Cancer Institute, 1987.
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9. American Cancer Society. Cancer of the colon and rectum: Summary of a public attitude survey. CA 1983; 33:359-365. 10. Knight KK, Fielding JE, Battista RN. Occult blood screening for colorectal cancer. JAMA 1989; 261:587-593. 11. Selby JV, Friedman CD. U.S. Preventive services task force, recommendations for sigmoidoscopic screening. JAMA 1989; 261:594. 12. Fleischer DE, Goldberg SB, Browning TH, Cooper JN, Friedman E, Goldner FH, Keeffe EB, Smith LE. Detection and surveillance of colorectal cancer. JAMA 1989; 261:580-585. 13. Canadian Task Force on the Periodic Health Examination. The periodic health examination: 2. 1989update. Can Med Assoc J 1989; 141:209-216. 14. Canadian Task Force on the Periodic Health Examination. Can Med Assoc J 1979; 121:146. 15. Lurie N, Manning WC, Peterson C, er al. Preventive care: Do we practice what we preach? Am J Public Health 1987; 77:801-804. 16. Gallup Organization, Inc. The 1987 Survey of Public Awareness and Use of Cancer Detection Tests. Princeton: The Gallup Organization, Inc., 1988. 17. Chao A, Paganini A, Ross RK, Henderson BE. Use of preventive care by elderly. Prev Med 1987; 16~710-722. 18. Andersen R, Aday LA. Access to medical care in the U.S.: Realized and potential, Med Care 1978; 16533-546. 19. Burack RC, Liang J. The early detection of cancer in the primary-care setting: Factors associated with the acceptance and completion of recommended procedures. Prev Med 1987; 16~739-751. 20. Hayward RA, Shapiro MF, Freeman HE, Corey CR. Who gets screened for cervical and breast cancer. Arch Intern Med 1988; 14&l 177-1181. 21. Macrae FA, Hill DJ, et al. Predicting colon cancer screening behavior from health beliefs. Prev Med 1984; 13:115-126. 22. Shah BV, Folsom RE, Harrell FE, Dillard CN. Survey Data Analysis Software for Logistic Regression. Research Triangle Park, NC: Research Triangle Institute, 1984. 23. Hosmer DW, Lemeshow S. Applied Logistic Regression. New York: Wiley, 1989. 24. Mitchell JB, Wedig G, Cromwell J. Medicare physician fee freeze. Health Aff 1989; 821-33. 25. Berger MC, Leigh JP. Schooling, self-selection, and health. J Human Resources 1988; 14~433-455. 26. Fuchs VR. Time preference and health: An exploratory study. In: Fuch VR, Ed. Economic Aspects of Health. Chicago: Univ. of Chicago Press, 1982. 27. Luft HS. Why do HMOs seem to provide more health maintenance services? Milbank Memorial Fund Q 1978; 56140-168.