1 Northern California Cancer Center, Union City, CA.
2 Center for Aging in Diverse Communities, Medical Effectiveness Research Center for Diverse Populations, Division of General Internal Medicine, Department of Medicine, University of California San Francisco, San Francisco, CA.
3 Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, CA.
4 Biostatistics Core, University of California San Francisco Cancer Center, San Francisco, CA.
Received for publication September 27, 2002; accepted for publication January 24, 2003.
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ABSTRACT |
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case-control studies; epidemiologic methods; ethnic groups; investigative techniques
Abbreviations: Abbreviations: HCFA, Health Care Financing Administration; RDD, random digit dialing.
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INTRODUCTION |
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Lung cancer is the leading cause of cancer mortality in the United States for both men and women (3). This paper reports strategies used to recruit African Americans, who on average bear a disproportionate burden of lung cancer, and Latinos, who have relatively lower rates of the disease. For example, in the San Francisco Bay Area of California from 1995 to 1999, the age-adjusted lung cancer incidence rates per 100,000 population were 65 for White, non-Hispanics; 80 for African Americans; and 36 for Hispanics (4). Ethnic differences in lung cancer incidence and survival have yet to be adequately explained and probably reflect environmental, lifestyle, biologic, and genetic influences. Comparing the effects of these factors in a very low-risk and a very high-risk population may help clarify how these factors interact to influence lung cancer risk. Elucidating the interplay of these factors is crucial to developing intervention and prevention strategies.
Both Latinos and African Americans have traditionally been underrepresented in health research. Therefore, there are limited data on the effectiveness of various recruitment strategies in these groups (513) and questionable generalizability of risk factors for lung cancer observed in previous case-control studies conducted in primarily White populations. In a previous lung cancer susceptibility study, which included African Americans and Caucasians in Los Angeles, California, controls were recruited through a combination of Department of Motor Vehicle records and Health Care Financing Administration (HCFA) listings (5); the investigators enrolled about 22 percent of the original group of potential controls identified or 26 percent of those not determined to be ineligible. They did not break down the results of control recruitment by ethnic group. More information is needed on the challenges and successes associated with the use of various recruitment methods in ethnically diverse populations.
The main purpose of this case-control study (19982001) was to examine genetic, behavioral, and occupational factors of potential etiologic significance in the occurrence of lung cancer among San Francisco Bay Area African Americans and Latinos. In this interim report, we briefly report on recruitment results for the lung cancer cases, but our emphasis is on comparing population- and community-based methods of recruiting controls. We compare 1) the effectiveness, by ethnic group, of the recruitment methods used; and 2) control groups on demographic characteristics and lung cancer risk factors across method of recruitment and with lung cancer cases to evaluate potential bias introduced by recruitment method.
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MATERIALS AND METHODS |
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Our initial approach was to use random digit dialing (RDD); telephone interviewers were fluent in both Spanish and English. However, because of the limited number of potentially eligible elderly African-American and Latino subjects identified through RDD, we turned to HCFA beneficiary records to identify controls aged 65 years or older. When these two population-based methods failed to yield sufficient numbers of eligible controls, we began community-based recruitment methods targeting churches, health fairs, senior centers, university employees, and patients of primary care physicians serving African Americans and Latinos.
To obtain eligible controls through RDD (13), we generated numbers based on 1997 listings for lung cancer cases provided by the Northern California Cancer Center for the five Bay Area counties (Alameda, San Francisco, Contra Costa, San Mateo, and Santa Clara). To generate these numbers, we used the telephone numbers (area code and first five digits) of the case listing, then we randomized the last two digits to achieve telephone numbers matching on county of residence. We also purchased from a vendor listed population-based samples, matching on age, ethnicity, gender, and county of residence. Telephone calls were made to enumerate the households; to ascertain the age, gender, and ethnicity of residents; and to obtain names and mailing addresses.
HCFA provided the name, address, age, gender, and ethnicity, but not the telephone number, of African-American and Latino beneficiaries living in the five Bay Area counties. We randomly selected 400 eligible participants and sent them letters on HCFA stationery introducing the study. A letter from the study team followed, explaining the nature of the study and requesting, on a reply/refusal postcard, a telephone contact number. For potential participants who did not decline via postcard, we conducted computer searches for telephone numbers and conducted home visits when searches for telephone numbers were not successful.
We developed community-based recruitment strategies targeting faith-based institutions (churches), health fair attendees, senior centers (housing and community centers), university employees, and physicians serving African Americans and Latinos. Working through established community linkages, an ethnically diverse staff of interviewers and outreach workers provided group and individual-level presentations and disseminated informational flyers and study brochures at church seminars, health fairs, and senior centers. Patients identified by their physician were sent letters of information about the study, and recruitment letters were sent via campus mail to African-American and Latino university employees.
Recruitment of lung cancer cases
Cases were ascertained from those reported to the Northern California Cancer Center, a population-based Surveillance, Epidemiology, and End Results cancer registry. Rapid case ascertainment methods, which consist of on-site medical record abstraction by trained registry staff, were used to maximize the chances of contacting cases prior to death. Although Surveillance, Epidemiology, and End Results files include ethnicity, rapid case ascertainment does not, and telephone screening was necessary to identify the ethnicity of cases. Eligibility criteria for lung cancer cases included 1) self-identified Latino or African-American ethnicity; 2) residence in Alameda, San Francisco, Contra Costa, Santa Clara, or San Mateo counties; 3) age of 21 years or older; and 4) a presumptive diagnosis of primary lung cancer. Decedents were not eligible for study participation, and proxy interviews were not conducted. Interview information and biologic samples (buccal smears and blood samples) were collected at a site selected by the participant, generally the residence.
For lung cancer cases, a letter was sent to the physician of record advising that the patient would be contacted to participate in the study and asking the physician to contact the researchers if there were any contraindications to the patients participation. If no response was received from the physician, the patient was sent a letter from the research team with a return acceptance/refusal postcard. Patients who did not refuse via postcard were then contacted by telephone by a language-matched interviewer to determine their ethnicity and assess their interest in participating in the study.
Tracking procedures
A computerized tracking system was used to examine the disposition of each potential case and control by ethnicity and method of recruitment. To assess the effectiveness of the various methods used to recruit controls from each ethnic group, we tracked the number in the original sampling frame (where available), the number successfully contacted, the number completing an eligibility interview, the number eligible for the study, and the number completing the full interview (including biologic samples). For controls, we also maintained a log of recruiting hours spent by recruitment method. We divided the total number of hours spent for each method by the number of controls resulting from that method to calculate the average number of interviewer hours per control interviewed for each recruitment method.
Data analysis
We compared characteristics of interviewed controls by method of recruitment to determine differences and similarities with respect to demographic and socioeconomic factors, smoking history, and smoking pack-years (1 pack-year = smoking the equivalent of one pack of cigarettes per day per year; e.g., 40 pack-years could be one pack a day for 40 years or two packs a day for 20 years) as well as occupational asbestos exposure history related to lung cancer risk. For Latinos, we also compared birthplace and English language fluency. In addition, we compared controls with cases regarding the same characteristics. Analyses were stratified by ethnicity. Analysis of variance was used to assess differences in continuous variables, and logistic regression was used to compare binary variables after adjusting for age and gender effects (except for age and gender comparisons).
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RESULTS |
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Recruitment of lung cancer cases
Of the initial 5,329 primary lung cancer cases identified through rapid case ascertainment, 732 were determined eligible by race/ethnicity; 470 were African American and 262 were Latino. These figures represent study ascertainment of eligible Latino and African-American cases during the period September 1, 1998July 11, 2001. Of persons with lung cancer reported by the registry, 53.4 percent self-identified as being in other ethnic groups, mainly White, non-Latino. We were unable to establish the ethnicity of almost one third of the reported cases because of incorrect contact information, inability to reach potential respondents, or refusal by potential respondents or their physicians (table 4).
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DISCUSSION |
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We were unable to meet control recruitment goals in a timely and cost-effective manner by using standard population-based methods. This problem was due to the age and ethnic distribution of eligible controls in the population. RDD required a tremendous amount of effort for a low yield of eligibles identified. However, a majority of eligible persons identified agreed to participate (62.3 percent). The HCFA method, on the other hand, was an excellent way to identify people who were eligible, but it was only marginally successful as a means of enrolling participants (21.4 percent). These results were expected given that information on ethnicity was not available for RDD until potential participants were screened; for HCFA, ethnicity but no telephone numbers were included in beneficiary records.
Community-based methods were much more effective than RDD and HCFA methods in enrolling eligible Latinos and African Americans since we were able to select sites with high concentrations of our targeted populations. Nevertheless, much work is still needed in future studies to determine optimal and valid recruitment methods for minorities.
After we adjusted for age, African-American controls recruited by using HCFA methods tended to be heavier smokers and longer-term smokers than those recruited through the other two methods. African-American community-based controls may be more representative of the general San Francisco Bay Area African-American population; HCFA beneficiaries represent only those aged 65 years or older, and RDD controls were persons who could be contacted by telephone. African-American cases appeared to be less educated than African-American controls and had higher numbers of smoking and occupational risk factors for lung cancer, as would be expected.
Latino community-based controls were less likely to be US born but tended to be better educated than RDD and HCFA controls. Despite these sociodemographic differences between Latino controls and cases, they were similar in terms of occupational factors that are putative lung cancer risk factors but demonstrated expected differences in tobacco-related risk factors. Latino cases tended to be older, which might explain why they tended to be less educated relative to Latino controls; that is, there may have been some residual confounding with age. Similar to the African Americans, Latino cases demonstrated a higher level of smoking-related risk factors than controls did, although they did not differ regarding occupational factors.
Studies suggest that people of lower socioeconomic status and those from minority groups may be less likely to respond to traditional recruitment efforts than those of higher socioeconomic status or nonminorities and are underrepresented in health research (8). There is some evidence pertaining to factors associated with the lower participation rates of diverse ethnic groups but little evidence about the effectiveness of specific recruitment methods. Barriers to recruitment and lack of study response may be attributable to a number of factors, including negative attitudes and beliefs about research, mistrust of researchers, lack of culturally and linguistically competent staff and recruitment processes, and limited representation of minority health researchers (912). These results demonstrate differences in success rates in the recruitment of controls comparing two population-based methods (RDD and HCFA) with community-based, nonprobabilistic, and non-population-based sampling methods. Community-based strategies involving initial contact by in-person presentations and/or face-to-face discussions were more effective than traditional population-based recruitment methods, which involved initial contact by telephone. Through face-to-face contact, study outreach staff may have overcome some of the barriers to recruitment, as evidenced by the higher yield of controls recruited by using community-based methods.
Although use of probabilistic methods is intended to help guard against sampling bias, the lower percentages of eligible participants recruited by using specific population-based methods (62 percent for RDD and 21 percent for HCFA) calls into question the representativeness of controls obtained by using these methods. Therefore, we resorted to community-based methods, which also have a potential for sampling bias.
Screening of potential cases provided by the tumor registry for eligibility regarding ethnicity required a large effort since less than 14 percent of the sampling frame was eligible for the study. Additionally, lung cancer mortality made recruitment especially challenging among Latinos and African Americans; approximately 40 percent were deceased when we attempted to contact them, even though rapid case ascertainment was used. However, of those living cases with whom we established contact, participation rates were fairly good (68 percent for Latinos and 72 percent for African Americans), and participant refusal rates were relatively low (8 percent for African Americans and 9 percent for Latinos).
It would be valuable to know what biases were introduced by the use of community-based methods. Our study may be limited because we used nonrandom methods to select controls and because of biases potentially introduced by using these methods. When we compared selected characteristics of our population of controls with those of the population of our targeted five-county area, we learned that educational status and average household size were comparable. However, study controls tended to have a lower median household income and were less likely to be single. US Census data for our five-county area were readily available only on income for persons aged 15 years or older and on education for those aged 25 years or older. Thus, differences between study controls and the US Census data for the five counties might be explained partially by the older age distribution of our control population because of matching to cases on age (14). In future studies that involve resorting to non-population-based methods to recruit controls, investigators will need to exercise caution and collect data that may facilitate assessment of selection bias and potential confounding introduced by such nonrandom sampling methods.
Our results highlight the effectiveness of using alternative methods to recruit African-American and Latino participants into a case-control study of lung cancer susceptibility. Our willingness to try alternative recruitment strategies resulted in greater research participation. When traditional population-based methods failed to yield adequate numbers of controls, we explored the use of community-based recruitment methods to locate subjects who historically have been difficult to recruit. By using the talents of a diverse team and established community linkages, we identified and tapped into an eligible subject pool and successfully met recruitment goals for controls matched to cases on age, ethnicity, gender, and county of residence.
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ACKNOWLEDGMENTS |
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The authors are indebted to the study interviewers and outreach staff, Starr Amrit, Lizette Alvarez, Dr. Maria Diaz, Latonya Goodson, Doris de Leon, Dr. Wendy Lorizio, Dr. Julie Madsen, Nkem Ogbechie, Csaba Polony, Natalia Ramirez, James Taylor, and Jaime Wong-Dominguez.
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NOTES |
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REFERENCES |
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