Recruiting healthy participants for a large clinical trial

Recruiting Healthy Participants for a Large Clinical Trial Cathy Rudick, BPE, Nicholas R. Anthonisen, MD, and Jure Manfreda, MD Department of Medicine, University of Manitoba, and Health Sciences Centre, Winnipeg, Manitoba, Canada, R3A 1R9

ABSTRACT: The Lung Health Study (LHS) is a multicenter randomized clinical trial evaluating treatments for the prevention of chronic obstructive pulmonary disease (COPD). Participants are otherwise healthy smokers with borderline abnormal lung function, who are at relatively high risk of developing COPD. LHS recruiting efforts in the city of Winnipeg, Canada, resulted in the screening of 9,062 people (21% of age-eligible smokers) and randomization of 577 participants. Approximately 50% of the screenees were obtained by direct mail with follow-up telephone calls, while another 14% of the screenees were obtained at worksites. Other recruiting methods included use of mass media, passive displays at community events, and interviewer-aided mall recruiting. Screening rates (percent of the total age-eligible population in Winnipeg screened) were inversely related to age, although eligibility rates were directly related to age. Screening rate was inversely related to indicators of socioeconomic status independent of smoking status. However, randomization rates (percent of the ageeligible population which was randomized) were directly related to socioeconomic status, in part because exclusions for medical reasons were also inversely related to socioeconomic status. Eligibility at initial screening was not related to the recruiting method, but the likelihood of randomizing eligible participants was significantly greater at this clinic for those recruited via mass media and workplace screening than for those recruited by direct mail, and significantly less when recruited at community events. KEY WORDS: Recruiting, clinical trial, COPD

INTRODUCTION The University of Manitoba in W i n n i p e g w a s o n e of 10 centers in N o r t h America participating in a r a n d o m i z e d clinical trial a i m e d at e v a l u a t i n g strategies to p r e v e n t chronic obstructive p u l m o n a r y disease (COPD). The p r i m a r y objective of the L u n g H e a l t h S t u d y (LHS) w a s to d e t e r m i n e w h e t h e r a combination of s m o k i n g i n t e r v e n t i o n a n d use of an inhaled b r o n c h o d i l a t o r (iprat r o p i u m b r o m i d e ) w o u l d significantly slow the rate of decline of l u n g function

Address reprint requests to J. Manfreda, MD, Respiratory Hospital, 810 Sherbrook Street, Winnipeg, Manitoba R3A 1R8 Canada.

68S 0197-2456/93/$6.00

Controlled Clinical Trials 14:68S-79S (1993) © Elsevier Science Publishing Co., Inc. 1993 655 Avenue of the Americas, New York, New York 10010

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in middle-aged cigarette smokers who are at high risk for developing COPD [11. Each LHS center was charged with randomizing 600 participants over an 18-month period. In Winnipeg, 608 participants were recruited by screening approximately 9500 individuals, of w h o m 95% (577 participants and 9062 screenees) resided within the city limits. The present analysis includes only Winnipeg residents, since recruiting in the city was systematic and Winnipeg demographics were known. The objective of this paper is (1) to report on recruitment in Winnipeg, and (2) to determine the population characteristics associated with higher screening and randomization rate, and (3) to assess recruitment strategies with respect to the number of participants screened and randomized.

METHODS Population The age-eligible (35--59 years) population for the study was identified through the population registry of the Manitoba Health Services Commission (MHSC), the organization that administers both the provincial health insurance plan and the population registry in which all permanent residents of the province are listed. The population of Winnipeg at the beginning of recruitment was 625,304 of which 171,602 (27%) were between the ages of 35 and 59; of these 51% were females and 49% males [2]. The age-eligible individuals lived in 108,620 households, averaging 1.6 age-eligible subjects per household (MHSC, personal communication). Winnipeg is divided into 36 postal code areas. Smaller postal code areas were combined with adjacent ones to create 26 areas with populations of at least 3000 age-eligible individuals. Statistics Canada divides Winnipeg into 148 census tracts [2], which can be combined into postal code areas. Demographics and socioeconomic characteristics obtained during the 1986 census were available for both census tracts and for postal code areas [2,3]. Smoking prevalence was assessed in 20 of 26 areas in the course of telephone recruitment; age-eligible individuals who were contacted were questioned regarding smoking habits.

Screening The eligibility and exclusion criteria and screening methods for the Lung Health Study are presented elsewhere in detail [1]. Briefly, participants were smokers, aged 35-59, who were in good health and had a forced expired volume in 1 sec (FEV1) that was 50-90% of predicted normal [4] and less than 70% of the forced vital capacity. They were identified at an initial screening visit and asked to return for a second visit where lung function testing was repeated and potential participants were excluded for medical reasons or excessive alcohol intake. Participants underwent final lung function testing at a third visit and eligible individuals were then randomized. At any stage, eligible participants could refuse further testing and participation in the study.

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c. Rudick et al.

Recruitment Methods and Implementation Projections for Winnipeg based on previous population studies [5] indicated that between 9000 and 10,000 individuals about 5% of the age-eligible population--would have to undergo the initial screening in order to randomize the required 600 subjects. Seven methods were used to attract people to the initial screening, and at the initial screening the primary method of recruitment was established and recorded for each screenee. Recruitment strategies were implemented uniformly across the city and were not adapted to area socioeconomic and cultural characteristics. Recruitment was monitored throughout the 18-month period. Methods that became ineffective, i.e., produced less than 10 screenees per half-day of screening, were discontinued and new strategies were introduced to maintain the screening process at the required rate. 1. Direct mail. Address labels for age-eligible individuals were purchased from the MHSC. The direct-mail campaign to all age-eligible individuals in the city was implemented 4 months into recruitment. Each age-eligible individual was mailed a personally addressed letter inviting smokers to participate in an initial screening at a convenient regional site. Mailings were organized by postal code areas. Seventeen batches of 5000-8000 letters were sent. The option to respond by either mail (self-addressed, postagepaid envelope provided) or telephone was given. A follow-up reminder card was mailed 2 weeks after the original letter of invitation. 2. Telephone. Calls were made to the people w h o received direct mail and whose telephone numbers could be found in a street directory. Calls were made by trained telephone interviewers 1-3 weeks after the reminder cards were mailed. The interviewers established whether the person was a smoker, invited smokers to participate, and scheduled an appointment when possible. Follow-up telephone calls were added to the direct-mail campaign 10 months into recruitment w h e n it became obvious that mail alone would not meet recruitment goals. Overall, potential participants in 20 of the 26 postal code areas (in which 79% of the age-eligible population resided) were telephoned over 11 months. Telephone numbers were identified for 65% of the individuals w h o received direct mail. A total of 33,324 households were reached, accounting for about 32% of all age-eligible subjects or 47% of those with a known telephone number. 3. Workplace screening. All 103 local companies and organizations employing 250 or more workers were invited by mail and personal contact to participate, and 54 held onsite screening sessions. Those willing to participate in a screening session that involved pulmonary function testing during working hours were provided with an information and implementation package. Contacting individual employees was the responsibility of management at the worksite [6]. Workplace screening was implemented first because it tapped the most readily accessible large source of age-eligible individuals. 4. Shopping mall recruitment. Mall-based market research interviewers were hired in one mall. These interviewers approached shoppers, identified willing, age-eligible individuals, and accompanied them to an onsite clinic for initial screening. Interviewer-aided shopping mall recruitment initially

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provided a good source of participants. However, after 10 months the number of screenees decreased to less than 10 per half-day of screening, and people complained of being approached more than once. Other malls would not allow their patrons to be approached individually. They did allow screening clinics at which shoppers initiated contact, but this passive recruitment was not effective and was discontinued. . Community events. Trade shows, community fairs, and health-related campaigns with high attendance in the previous year were approached to include an LHS display and screening clinic. Such passive recruitment was implemented on an irregular basis throughout the recruitment period. . Mass media. This method involved print and electronic announcements, public service advertising, an introductory press conference, television and radio interviews, paid print and radio advertising, an early results press conference (including participant testimonials), monthly news releases, and a final recruitment press conference. The various media strategies were implemented as evenly as possible throughout the recruitment phase. . Other strategies. These include medical referrals, participant referrals, and general householder mailings. Medical referrals involved informing area physicians of LHS eligibility requirements and requesting the referral of patients who met study criteria. Large clinics were provided with brochures and posters for displays in waiting areas. Unmanned displays were used at medical conferences and informational letters were sent to all family physicians. Participant referrals resulted from word-of-mouth encouragement by screenees' families, friends, and coworkers. Several householder mailings were tried in which LHS information was included with other notices such as parliamentary newsletters, billing notices, and householder coupon packages. In addition, service-oriented businesses such as banks were asked to provide space for LHS displays as a means of informing and recruiting participants to the study. RESULTS In Winnipeg, 9062 of 171,602 age-eligible individuals were screened, a screening rate of 5.3% (Table 1). There were slightly more males (4759 or 5.6%) than females (4303 or 5.0%) screened. The screening rate was inversely related to age in both sexes. For both males and females, the direct-mail approach was the most successful recruitment method: 1.9% of males and 1.6% of females in the respective age-eligible populations were recruited by this method (Table 1). Of the total number screened, 34.5% of the males and 31.6% of the females resulted from direct mail. The second most successful technique was follow-up telephoning, which had the same effectiveness (1.1% of age-eligible population screened) for both males and females. It contributed 20.3% of the males and 23.0% of the females screened. The combination of direct mail with telephone follow-up produced approximately 50% of screenees (Table 1). For both males and females, workplace screening was the third most successful recruitment approach: 0.8% of age-eligible males and 0.7% of ageeligible females were screened in the workplaces. Workplace screening contributed approximately 14% of all initial screenees. On the average, 2.3% of

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c . Rudick et al. S c r e e n i n g R a t e ( P e r c e n t a g e of T o t a l A g e - E l i g i b l e P o p u l a t i o n S c r e e n e d ) in Winnipeg Age 35-39 No.

Sex Males

Population Direct mail Follow-up telephone Workplace Shopping mall Community events Mass media Other Total screened

Females Population Direct mail Follow-up telephone Workplace Shopping mall Community events Mass media Other Total screened Both

Population Total screened

40-44 %

19,724 489 220 217 124 157 92 102 1,401

%

21,126 2.5 1.1 1.1 0.6 0.8 0.5 0.5 7.1

20,116 352 242 200 82 118 71 93 1,158

No.

45-49

363 249 142 132 104 59 92 1,141

325 237 159 108 94 53 95 1,071

%

15,919 1.7 1.2 0.7 0.6 0.5 0.3 0.4 5.4

21,381 1.8 1.2 1.0 0.4 0.6 0.4 0.5 5.8

No.

50-54

274 182 112 90 55 50 57 820

257 228 126 86 45 44 53 839

%

13,977 1.7 1.1 0.7 0.6 0.4 0.3 0.4 5.2

16,236 1.5 1.1 0.7 0.5 0.4 0.3 0.4 5.0

No.

55-59

270 158 114 80 30 23 39 714

247 164 88 81 44 44 42 710

%

13,998 1.9 1.1 0.8 0.6 0.2 0.2 0.3 5.1

14,286 1.6 1.4 0.8 0.5 0.3 0.3 0.3 5.2

No.

Total

247 158 84 86 31 43 34 683

178 117 64 66 26 36 36 523

%

84,744 1.8 1.1 0.6 0.6 0.2 0.3 0.2 4.9

14,839 1.7 1.2 0.6 0.6 0.3 0.3 0.3 5.0

No.

1,643 1.9 967 1.1 702 0.8 512 0.6 377 0.4 267 0.3 324 0.4 4,759 5.6 86,858

1.2 0.8 0.4 0.4 0.2 0.2 0.2 3.5

1,359 1.6 988 1.1 637 0.7 423 0.5 327 0.4 248 0.3 319 0.4 4,303 5.0

39,840 42,507 32,155 28,263 28,837 171,602 2,560 6.4 2,212 5.2 1,659 5.2 1,425 5.0 1,206 4.2 9,062 5.3

t h e e m p l o y e e s in p a r t i c i p a t i n g w o r k p l a c e s w e r e s c r e e n e d ; t h i s p r o p o r t i o n v a r i e d f r o m 0.5% to 6.5% a m o n g w o r k p l a c e s . T h e r e m a i n i n g s c r e e n e e s w e r e attracted by interviewer-aided shopping mall recruitment, mass media, miscellaneous community events, and other methods. T a b l e 2 s h o w s t h e o u t c o m e of s c r e e n i n g . M a n y s c r e e n e e s w e r e i n e l i g i b l e w i t h r e s p e c t to l u n g f u n c t i o n ; in o v e r 95% of c a s e s t h i s w a s d e t e r m i n e d at t h e first s c r e e n i n g w i t h t h e r e m a i n d e r b e i n g d e t e r m i n e d at t h e s e c o n d . Elig i b i l i t y in t e r m s of l u n g f u n c t i o n w a s 47% h i g h e r for m a l e s (20.9%) t h a n for f e m a l e s (14.2%) at all a g e s . F o r b o t h s e x e s , l u n g f u n c t i o n e l i g i b i l i t y i n c r e a s e d w i t h a g e . E x c l u s i o n s for m e d i c a l r e a s o n s o r e x c e s s i v e a l c o h o l i n t a k e i n c r e a s e d w i t h a g e a n d a g r e a t e r f r a c t i o n of l u n g f u n c t i o n - - e l i g i b l e m a l e s t h a n f e m a l e s (29.9% vs. 19.9%, r e s p e c t i v e l y ) w e r e e x c l u d e d . A p p r o x i m a t e l y 50% of t h e s e e x c l u s i o n s o c c u r r e d at t h e first s c r e e n i n g a n d 50% at t h e s e c o n d . T h e p r o p o r t i o n of l u n g f u n c t i o n - e l i g i b l e i n d i v i d u a l s w h o r e f u s e d f u r t h e r p a r t i c i p a t i o n w a s h i g h e r for f e m a l e s (44.4%) t h a n for m a l e s (34.1%). I n m a l e s , r e f u s a l s d e c l i n e d w i t h a g e , w h i l e in f e m a l e s it w a s n o t r e l a t e d to a g e . O f t h e s e r e f u s a l s , 73% w i t h d r e w a f t e r t h e first s c r e e n i n g , 26% a f t e r t h e s e c o n d , a n d l e s s t h a n 1% a f t e r t h e t h i r d visit. A b o u t 36% of l u n g f u n c t i o n - e l i g i b l e s c r e e n e e s of e a c h sex w e r e r a n d o m i z e d . T h e a g e - e l i g i b l e p o p u l a t i o n i n t h e 26 a r e a s o f W i n n i p e g r a n g e d f r o m 3041 to 11,537 w i t h a m e d i a n of 6204. T a b l e 3 s h o w s t h e v a r i a t i o n a m o n g a r e a s in s e l e c t e d s o c i o e c o n o m i c c h a r a c t e r i s t i c s for all a g e s d e r i v e d f r o m c e n s u s d a t a

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Winnipeg Recruiting for the Lung Health Study Table 2

Screening O u t c o m e Lung FunctionEligible ~

Excluded

Refused

Randomized

Age

Number screened

%

No.

%

No.

%

No.

%

Male

35-39 40 ~ 45--49 50-54 55-59 Total

1401 1141 820 714 683 4759

136 197 196 203 262 994,

9.7 17.3 23.9 28.4 38.4 20.9

33 49 65 61 89 297

24.3 24.9 33.0 30.0 34.0 29.9

53 70 69 66 81 339

39.0 35.5 35.0 32.5 30.9 34.1

50 78 62 76 92 358

36.8 39.6 31.5 37.4 35.1 36.0

Female

35-39 40 ~ 45-49 50-54 55-59 Total

1159 1071 839 711 523 4303

84 118 134 141 136 613

7.2 11.0 16.0 19.8 26.0 14.2

13 20 33 21 35 122

15.5 16.9 24.6 19.9 25.7 19.9

39 48 57 73 55 272

46.4 40.7 42.5 51.8 40.4 44.4

32 50 44 47 46 219

38.1 42.4 32.8 33.3 33.8 35.7

Both

Total

9062

1,607

17.7

419

26.1

611

38.0

577

35.9

Sex

No.

aLung function-eligible are expressed as percentage of the total number of screened individuals. Randomized, excluded, and refused are expressed as percentage of the lung function-eligible participants.

plus smoking habits of age eligibles from the t e l e p h o n e survey. Most of these characteristics, including smoking, varied two- to sevenfold a m o n g areas. The percentages of the age-eligible p o p u l a t i o n screened, excluded, and r a n d o m i z e d (screening, exclusion, r a n d o m i z a t i o n rate, respectively) w e r e calculated separately for each of the 26 areas. The screening rate varied from 3.7% to 6.2% (median 5.2%) and the r a n d o m i z a t i o n rate from 0.04% to 0.48% (median 0.33%). The screening rate was also calculated for each recruiting m e t h o d within each area. The screening rates d u e to mass media, c o m m u n i t y events, a n d workplace recruitment s h o w e d little variation a m o n g areas. The screening rates resulting from direct mail and t e l e p h o n e follow-up varied substantially b y area. O v e r time, the r e s p o n s e to direct mail declined, probably because willing residents were recruited b y other m e t h o d s . The screening rate for each area before mailings correlated negatively with the direct-mail screening rate for each area: a 1% higher premail screening rate in an area resulted in a 0.5% lower screening rate in r e s p o n s e to direct mail. In order to d e t e r m i n e the relationship b e t w e e n area p o p u l a t i o n characteristics and recruitment, screening, direct-mail screening, exclusion, refusal, and r a n d o m i z a t i o n rates were c o m p a r e d to the area socioeconomic characteristics b y linear regression a n d results are s h o w n in Table 4. Both the screening and direct-mail screening rates increased significantly with the p r o p o r t i o n of individuals filing tax returns below $15,000, the p r o p o r t i o n of individuals with less than grade 9 education, and with the prevalence of s m o k i n g in the area. O n the other h a n d , they both declined with increased p r o p o r t i o n of individuals with some university education. For example, a 30% increase in p e o p l e with some university education (the range of variability b e t w e e n areas in Table 3) was associated with approximately a 1% lower screening rate. Even after controlling for the effect of smoking with multiple regression anal-

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c. Rudick et al.

Table 3

S u m m a r y of Socioeconomic Characteristics of W i n n i p e g Areas Area Population Value

Variable (%)

Number of Areas

Median

Minimum

Maximum

Nonofficial language Owned dwellings Single-person households Income tax tilers <$15,000 Male ever married Female ever married Grade 9 education Some university Smoking

26 26 26 26 26 26 26 26 20

14.8 61.4 23.6 48.0 51.8 53.8 14.3 18.7 24.0

7.9 4.3 9.1 36.0 19.8 17.9 6.0 7.8 12.4

39.5 88.2 66.0 78.0 64.6 64.4 32.8 41.4 53.7

Table 4

Relationship B e t w e e n Area Characteristics a n d the Recruiting Process

Area Population Characteristic (%)

Screening Rate

Direct Mail Screening Rate

Exclusion Rate

Refusal Rate

Randomization Rate

Nonofficial language Owned dwellings Single person households Income tax tilers <$15,000 Male ever married Female ever married < Grade 9 education Some university Smoking

0 0 0 + 0 0 + +

0 0 0 + 0 0 + +

0 0 + 0 0 + 0 0

0 0 0 0 0 0 0 0 0

0 0 0 0 0 0

0 = no relationship; + = significant (p < .05) direct relationship; - = significant (p < .05) inverse relationship.

ysis, the screening rate w a s positively correlated with u s e of nonofficial lang u a g e a n d w i t h the p r o p o r t i o n of p e o p l e w i t h less t h a n g r a d e 9 e d u c a t i o n a n d negatively correlated w i t h the p r o p o r t i o n h a v i n g s o m e u n i v e r s i t y education. O n the other h a n d , the r a n d o m i z a t i o n rate w a s significantly inversely related to the p r o p o r t i o n of p e o p l e u s i n g the nonofficial l a n g u a g e s (neither French nor English), to the p r o p o r t i o n of l o w - i n c o m e tax fliers, a n d to the p r o p o r t i o n of p e o p l e w i t h less t h a n g r a d e 9 education. While there w a s no significant relationship o b s e r v e d b e t w e e n area characteristics a n d refusal rate, the exclusion rate increased significantly w i t h b o t h the p r o p o r t i o n of lowi n c o m e p e o p l e a n d those w i t h less t h a n g r a d e 9 e d u c a t i o n in the area. In addition, the exclusion rate w a s inversely related to the p r o p o r t i o n of privately o w n e d dwellings. Table 5 s h o w s the o u t c o m e of screening b y r e c r u i t m e n t m e t h o d . The proportion of lung function--eligible screenees w a s the lowest a m o n g those screened at miscellaneous c o m m u n i t y e v e n t s (12.9%) followed b y w o r k p l a c e s (15.3%). T h e r e w a s also a substantial variability in the p e r c e n t a g e of participants w h o w e r e excluded a n d w h o r e f u s e d to participate. W o r k p l a c e screening, for exa m p l e , h a d the h i g h e s t p r o p o r t i o n of eligible subjects w h o w e r e r a n d o m i z e d

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Winnipeg Recruiting for the Lung Health Study

Table 5

O u t c o m e of Screening b y Recruitment M e t h o d

Method Direct mail Follow-up telephone Workplace Shopping mall Community events Mass media Other

Lung FunctionScreened E ~ b l e " No. No. % 3002 1955 1309 935 704 515 633

549 375 200 190 91 91 110

18.3 19.2 15.3 20.3 12.9 17.7 17.4

Excludedb Refusal b No. % No. % 194 109 31 21 15 22 27

35.3 29.1 15.5 11.1 16.5 24.2 24.5

162 152 66 113 56 27 34

29.5 40.5 33.0 59.5 61.5 29.7 30.9

Randomized b No. % 193 114 103 56 20 42 49

35.2 30.4 51.5 29.5 22.0 46.2 44.5

a% lung function-eligible is a percentage of the number screened. b% Randomized, % excluded, and % refused are percentages of lung function-eligible participants.

(51.5%) and relatively low proportions of those w h o w e r e excluded (15.5%) or refused to participate (33.0%). In order to examine the relationships b e t w e e n recruitment m e t h o d a n d lung function eligibility or willingness to be r a n d o m i z e d , multiple logistic regression [7] analysis was carried out (Table 6). First, all screened subjects g r o u p e d b y recruitment m e t h o d were e n t e r e d into the model, with lung function eligibility status as the d e p e n d e n t variable. For c o m p a r i s o n of recruitment m e t h o d s , the direct-mail m e t h o d was used as a reference. In addition, age and sex were a d d e d to the model because t h e y w e r e significantly associated with lung function eligibility. W h e n age and sex were a c c o u n t e d for, eligibility did not differ b e t w e e n individuals recruited by different methods. Similar analysis was p e r f o r m e d to examine the relationship b e t w e e n recruitment m e t h o d and participants r a n d o m i z e d (Table 6). For this analysis, only lung function-eligible subjects were e n t e r e d into the m o d e l a n d the d e p e n d e n t variable was r a n d o m i z a t i o n status. Probability of r a n d o m i z a t i o n of lung function eligibles was significantly related to recruitment m e t h o d . Lung function-eligible individuals recruited in the workplace (OR = 1.95, 95% CI = 1.40, 2.71) or b y mass media (OR = 1.58, 95% CI = 1.01, 2.47) w e r e more likely to be r a n d o m i z e d than those recruited by mail. O n the other h a n d , those recruited at c o m m u n i t y events were significantly less likely to be r a n d o m i z e d (OR = 0.50, 95% CI = 0.43 and 0.85).

DISCUSSION Because a relatively small population was available, recruitment in Winnipeg was a formidable task. Over an 18-month period we screened over 9000 individuals, or 5.3% of the age-eligible population. A high p r o p o r t i o n (21%) of age-eligible smokers was screened if the prevalence of smoking was 25% as estimated by o u r t e l e p h o n e survey. We were aware that multiple recruitment strategies w o u l d be required and initially p l a n n e d to d e p e n d chiefly o n workplace screening, direct mail, a n d

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C. Rudick et al. Table 6

Odds Ratios (OR) and Confidence Intervals (CI) for Eligibility and for Randomization Eligible

Variable

Randomized

95% CI

OR

95% CI

Direct maila Follow-up telephone Workplace Shopping mall Community events Mass media Other

OR 1.00 1.07 0.87 1.12 0.83 1.02 1.06

0.92-1.24 0.73-1.05 0.92-1.35 0.65-1.06 0.90-1.32 0.84-1.34

1.00 0.81 1.95 0.77 0.50 1.58 1.48

0.61-1.08 1.40-2.71 0.53-1.09 0.43-0.85 1.01-2.47 0.98-2.24

Age Male sex

1.08 1.70

1.07-1.09 1.51-1.90

0.99 --

0.97-1.00 --

aReference categoryfor other recruitmentmethods. the media. Interviewer-aided mall recruiting became available as the study began, and the telephone follow-up strategy [8] was developed later. With our principal and most productive method, direct mailing, we screened 1.8% of the age-eligible population and identified 33% of screenees. This proportion increased to approximately 50% when combined with follow-up telephoning. With telephoning, we screened 1.14% of the age-eligible population by contacting approximately one-third of them. For another third a telephone number was not easily available, and for the remaining third of the population we could not establish contact although we had a telephone number. Workplace screening was implemented early and produced about 15% of screenees by screening in 54 of 103 companies with more than 250 employees, reaching more than half of the labor force in these companies. The large variability among companies in the proportion of employees screened (from 0.5% to 6.5%) was likely due to a number of factors. Screening was more successful in smaller than in larger workplaces; 3.5% of employees were screened from firms with 250-1000 employees and 1.9% were screened from firms with more than 1000 employees. The considerable organization and planning required for workplace screening [9] was more difficult to achieve in larger companies and was dependent on the enthusiasm of the worksite organizers whatever the size of the company. We considered recruiting in companies with less than 250 employees, but the costs in staff and setup time would have been too high for the small number of eligible and interested employees. To justify setting up a screening facility at a worksite, we required a good prospect of a half-day's work, or at least 10 screens. Given a screening rate of 3.5%, a work force of less than 250 would not fulfill this requirement. Early in recruitment we had good results with interviewer-aided recruitment in one shopping mall. When a passive approach was utilized in shopping malls, i.e., setting up a clinic with posters dependent on potential participants initiating contact, few volunteers were attracted. This approach was useful only at community fairs catering to large groups of people indulging in leisure activities. Even so, such recruiting was associated with very high refusal, as was interviewer-aided mall recruiting. Mass media did not produce large numbers of initial screens. This differed

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from most other LHS centers and may be related to the cultural characteristics of our population [10]. Because of Canadian universal health insurance and the associated availability of medical care, the LHS screening did not offer a uniquely free benefit in terms of lung function testing. Although mass media and miscellaneous advertising activities were not credited with many screenings, we nevertheless believe them to have been an important part of our program. They provided the "background" by creating a general awareness of our presence in the community [9] and enhanced the effectiveness of more targeted recruitment strategies involving direct contact with potential participants [11]. In Winnipeg the screening rate varied by area. Our data indicate that some of this variability was explained by differences in the socioeconomic characteristics of the populations residing in these areas. Both overall and directmail recruitment were more successful in less affluent areas of the city. Although in these areas smoking was more prevalent, the screening rate was associated with less education even when controlling for smoking. It seems unlikely that the message of our campaign appealed more to those with less income and education. A more plausible explanation might be that any antismoking intervention that is both free and institutional is more appealing to individuals with low income and education. Smoking cessation programs are not supported by Canadian health insurance, and it seems likely that the chief perception of potential benefit from LHS participation was smoking cessation. On the other hand, area characteristics that were associated with good screening rates were inversely related to randomization rate. We were less likely to randomize eligible screenees from less affluent areas, with less educated people and with a higher proportion of immigrants speaking a nonofficial language. Our data (Table 4) indicate that in less affluent areas with higher screening rates, fewer subjects were randomized because of more exclusions on medical grounds and not because of more refusals. While there was no association between the refusal rate and socioeconomic characteristics of areas, exclusion rates of eligible subjects increased with the proportion of low-income and low-education people and decreased with the proportion of privately owned dwellings. Data from our mail campaign revealed the interdependence of recruiting methods and the law of diminishing returns. The higher the screening rate in an area before letters were mailed out, the lower the effectiveness of direct mail. The same relationship was suggested for the screening rate from telephone follow-up. Among those eligible, age and particularly sex were not statistically significant predictors of randomization. However, the percentage of randomized participants varied substantially with recruitment method. Lung function eligibles identified in the workplace and through mass media were significantly more likely to be randomized than those identified by direct mail. Both exclusions and refusals were low for workplace screening, and screenees responding to mass media refused to participate (Table 5). On the other hand, those eligibles who were screened at community events had a lower probability of being randomized primarily because many refused (Table 5). Those recruited by telephone and by interviewers in a mall were more likely to

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c. Rudick et al.

Table 7

Effectiveness of Recruitment Strategies Effort Effort Strategy Volume (Organization) (Implementation) Workplace Moderate High Moderate Mass media Low Low Low Direct mail High Low Low Follow-up telephone High Moderate High Shopping mall Moderate Low High Community events Low Low Low

Richness Moderate Moderate Low Low Low Very Low

Richness (%) 7.9 8.2 6.4 5.8 6.0 2.8

refuse and less likely to be randomized than those contacted by direct mail. These methods were much more aggressive than the workplace, direct mail, and mass media approaches in that the initial contact between subject and recruiter was direct and personal. This suggests that while more aggressive methods may identify eligibles, the participant or screenee who actively takes the first step is more likely to be randomized. Aggressive methods may increase the screening rate but also may decrease the probability of randomization. In planning for recruitment, we considered the volume (how many initial screenings a particular strategy produced), effort (staff time), and richness (% randomized of those initially screened) of potential strategies (Table 7). It was relatively easy to organize interviewer-aided shopping mall recruitment and telephoning, but implementation required many hours of work by recruiters. On the other hand, the organizational effort of screening in workplaces was high because several levels of management and labor needed to be contacted and negotiated with. Direct mail was relatively easy to organize and implement; once the system was set up, letters could be sent with very little staff effort. Initially we expected a greater volume from workplace and community events screening and a lower volume from direct mail and telephoning. The experience was the opposite. Media and medical referrals were also much less effective than expected. On the other hand, we were surprised by the success of interviewer-aided shopping mall recruitment. Results of this analysis also suggest that the effectiveness of recruitment is influenced to some extent by the socioeconomic and cultural characteristics of the population, such as income, education, and immigrant status, in addition to the prevalence of smoking. This information could be used in two ways to improve future recruitment efforts. One way would be to target the recruitment efforts at areas with characteristics suggesting a better response. The other would be to tailor the recruitment effort and message to the socioeconomic characteristics of the population. Supported by NHLBIcontract no. 1-HR-46017and a grant from MRC Canada.

REFERENCES 1. Connett JE, Kusek JW, Bailey WC, O'Hara P, Wu M: Design of the Lung Health Study: a randomized clinical trial of early intervention for chronic obstructive pulmonary disease. This issue

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2. Statistics Canada: Census tracts. Winnipeg. Part 1: Profiles. Census 1986. Minister of Supply and Services Canada, 1988 3. Statistics Canada: Urban FSA and rural postal code summary data. Western provinces and the territories. Minister of Supply and Services Canada, 1987 4. Crapo RO, Morris AH, Gardner RM: Reference spirometric values using techniques and equipment that meet ATS recommendation. Am Rev Resp Dis 123:659644, 1981 5. Manfreda J, Nelson N, Cherniack RM: Prevalence of respiratory abnormalities in a rural and an urban community. Am Rev Resp Dis 117:215-226, 1978 6. Ogilvie JT, Mishkel NR, Mishkel MA, Welch VE, Insull W Jr, Probstfield JL, Gotto A: Occupational screenings: recruitment from private industry. Circulation 66(4):4043, 1982 7. Kahn MA, Sempos CT: Statistical methods in epidemiology. New York, Oxford University Press, 1989 8. Prout TE: Patient recruitment: other examples of recruitment problems and solutions. Clin Pharmacol Ther 25:695-696, 1979 9. Agras WS, Bradford RH, Hunninghake DB, Knoke J, Marshall G, McKeown M: Participant recruitment to the Coronary Primary Prevention Trial. J Chron Dis 36:451-65, 1983 10. Connett JE, Bjornson-Benson W, Daniels K: Recruitment of participants in the Lung Health Study, II: assessment of recruiting strategies. This issue 11. Agras WS, Bradford RH. Recruitment: an introduction. Circulation 66(4):2-5, 1982