Short Communication Factors Associated with Refusal to Provide a Buccal Cell Sample in the Agricultural Health Study Lawrence S. Engel, 1 Nathaniel Rothman, Charles Knott, Charles F. Lynch, Nyla Logsden-Sackett, Robert E. Tarone, and Michael C. Alavanja Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Bethesda, Maryland [L. S. E., N. R., R. E. T., M. C. A.]; Battelle’s Centers for Public Health Research and Evaluation, Durham, North Carolina [C. K.]; and Department of Epidemiology, College of Public Health, The University of Iowa, Iowa City, Iowa [C. F. L., N. L-S.] Abstract Epidemiological studies are increasingly collecting buccal cells and other sources of DNA for genetic analysis. However, high refusal rates raise concerns about possible selection bias. This study examines the subject characteristics associated with refusal or failure to provide a buccal cell sample. Subjects were male farmers in the Agricultural Health Study, which is being conducted in Iowa and North Carolina. As part of a 5- year follow-up, cohort members were contacted by telephone and asked to participate in a telephone interview and to consent to providing a buccal cell sample using a kit that was mailed to them. Demographic, lifestyle, disease, and occupational characteristics were compared between consenters who returned a sample (“compliers”), nonconsenters (“refusers”), and consenters who failed to return a sample (“noncompliers”). Compliers (n  8794), refusers (n  3178), and noncompliers (n  3008) were quite similar, although compliers tended to be slightly older. Although some significant differences between these groups were observed, the magnitude of these differences was generally small, usually no more than a few percentage points. In conclusion, this study found little difference between male farmers who agreed to provide buccal cell samples versus those who either refused to provide a sample or who agreed but failed to return the sample. Observed differences were typically small and would be unlikely to compromise etiologic associations identified in such a prospective study. In short, there appears to be little selection bias in the Agricultural Health Study buccal cell collection process, further supporting the use of such mailed collection kits in epidemiological research. Introduction Growing interest in genetic risk factors for disease, including direct gene effects and gene-environment interactions, has re- sulted in an increase in the collection of genetic material from subjects in epidemiological studies. Buccal cells are an increas- ingly common source of genetic material, in part because of the noninvasive means by which they can be obtained. Certain techniques of buccal cell collection also make possible the collection and shipment of the material via telephone and mail, substantially reducing study costs. This is especially important for many large prospective studies among dispersed popula- tions. In such cases, an increasingly frequent method involves mailing subjects a kit containing all of the necessary materials to store and mail back a sample. In all epidemiological studies, some eligible subjects will refuse to participate in some or all aspects of the study, poten- tially resulting in selection bias. In most studies involving mailed buccal cell collection, nonparticipation can occur either when a subject refuses the request to provide a sample or when a subject who consents to provide a sample fails to return the sample. These two forms of nonparticipation may be caused by different factors and may introduce different biases. It is im- portant for the design of epidemiological studies and the anal- ysis and interpretation of their results to identify such factors. The present study examines subject characteristics asso- ciated with refusal or failure to provide a buccal cell sample among participants in the Agricultural Health Study. Materials and Methods Subjects. Subjects consisted of male private pesticide appli- cators (primarily farmers) participating in the Agricultural Health Study, a prospective cohort study that has been de- scribed in detail elsewhere (1). The study cohort includes 52,400 farmers from Iowa and North Carolina, who were enrolled between 1993 and 1997. We are currently attempting telephone contact with all of the subjects as part of a 5-year follow-up. On contact, subjects are first asked if they will participate in a CATI. 2 If the subject agrees, then after the interview, the interviewer briefly explains to the subject the reason for collecting buccal cells, describes the “swish and spit” buccal cell collection technique (2), and asks if the subject is willing to participate. The subjects are encouraged by the in- terviewer to ask any questions they may have. Of the 22,079 farmers for whom contact was attempted by mid-July 2000, 72% agreed to the CATI, and 15% refused. The remaining subjects either could not be reached (12%) or were too ill to participate in the interview (1%). Buccal Cell Collection Technique. Subjects who consented to provide a buccal cell sample were mailed a kit containing a consent form, instructions for collecting and returning the sam- Received 8/17/01; revised 1/31/02; accepted 2/11/02. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 To whom requests for reprints should be addressed, at Occupational Epidemi- ology Branch, National Cancer Institute, 6120 Executive Boulevard, Room 8113, Bethesda, MD 20892-7240. Phone: (301) 402-7825; Fax: (301) 402-1819; E- mail: engell@mail.nih.gov. 2 The abbreviation used is: CATI, computer-assisted telephone interview. 493 Vol. 11, 493– 496, May 2002 Cancer Epidemiology, Biomarkers & Prevention on December 8, 2021. © 2002 American Association for Cancer Research. cebp.aacrjournals.org Downloaded from