Survey mode and asking about future intentions did not impact self-reported colorectal cancer screening accuracy

Self-reported colorectal cancer (CRC) screening behavior is often subject to over-reporting bias. We examined how the inclusion of a future intention to screen item (viz. asking about future intentions to get screened before asking about past screening) and mode of survey administration impacted the accuracy of self-reported CRC screening.

The target population was men and women between 49 and 85 years of age who lived in Olmsted County, MN, for at least 10 years at the time of the study. Eligible residents were randomized into four groups representing the presence or absence the future intention to screen item in the questionnaire and administration mode (mail vs. telephone). A total of 3,638 cases were available for analysis with 914, 838, 956, and 930 in the mail/future intention, mail/no future intention, telephone/future intention, and telephone/no future intention conditions, respectively. False positives were defined as self-reporting being screened among those with no documented history of screening in medical records and false negatives as not self-reporting screening among those with history of screening.

Comparing false positive and false negative reporting rates for each specific screening test among the responders at the bivariate level, regardless of mode, there were no statistically significant differences by the presence or absence of a preceding future intention question. When considering all tests combined, the percentage of false negatives within the telephone mode was slightly higher for those with the future intention question (6.7% vs 4.2%, p = 0.04). Multivariate models that considered the independent impact of the future intention question and mode, affirmed the results observed at the bivariate level. However, individuals in the telephone arm (compared to mail) were slightly (though not significantly) more likely to report a false positive (36.4% vs 31.8%, OR = 1.11, p = 0.55).

It may be that in the context of a questionnaire that is clearly focused on CRC and with specific descriptions of the various CRC screening tests, certain design features such as including intention to screen items or mode of administration will have very little impact on the accuracy of self-reported CRC screening.