Response rates in a case-control study: effect of disclosure of biologic sample collection in the initial contact letter.
OBJECTIVE
Participants in epidemiology studies are often asked to complete an interview and to provide biospecimens. In a population-based case-control study of kidney cancer involving an interview and optional biospecimens, we examined whether mentioning the biospecimens in the initial contact letter adversely affects willingness to be interviewed.


METHODS
Eligible cases (n = 434) and controls (n = 775) in Detroit were alternately assigned to receive one of two versions of the contact letter. Both explained that the study involves an interview with 100 dollars compensation plus an optional component with additional compensation; only one disclosed that the optional component involved biospecimens.


RESULTS
There were no meaningful differences between the groups in willingness to be interviewed. However, among 303 cases and 351 controls already interviewed, the proportion providing biospecimens was higher in the fully informed group: for blood, the differences were 10.8 (95% CI, 2.0, 19.5) for cases and 6.7% (95% CI, -1.7, 15.1) for controls. Findings were similar for saliva.


CONCLUSIONS
In a study involving an interview and optional biospecimens, informing people about the samples in the contact letter seems preferable to a non-specific reference to a second study component. Both approaches yielded similar interview participation rates, but biospecimen participation rates were higher among those informed about the samples in the contact letter.
Colt
Joanne S
JS
Occupational Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20852, USA. coltj@mail.nih.gov
Wacholder
Sholom
S
Schwartz
Kendra
K
Davis
Faith
F
Graubard
Barry
B
Chow
Wong-Ho
WH
D000328:Adult; D000368:Aged; D001800:Blood Specimen Collection / Q000523:psychology; D016022:Case-Control Studies; D015709:Correspondence as Topic; D030881:Disclosure / Q000592:standards*; D015981:Epidemiologic Factors; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015146:Midwestern United States; D010865:Pilot Projects; D012463:Saliva