Refusal to participate in research among hard-to-reach populations: The case of detained persons.

Providing insights on refusal to participate in research is critical to achieve a better understanding of the non-response bias. Little is known on people who refused to participate, especially in hard-to-reach populations such as detained persons. This study investigated the potential non-response bias among detained persons, comparing participants who accepted or refused to sign a one-time general informed consent. We used data collected in a cross-sectional study primary designed to evaluate a one-time general informed consent for research. A total of 190 participants were included in the study (response rate = 84.7%). The main outcome was the acceptance to sign the informed consent, used as a proxy to evaluate non-response. We collected sociodemographic variables, health literacy, and self-reported clinical information. A total of 83.2% of the participants signed the informed consent. In the multivariable model after lasso selection and according to the relative bias, the most important predictors were the level of education (OR = 2.13, bias = 20.7%), health insurance status (OR = 2.04, bias = 7.8%), need of another study language (OR = 0.21, bias = 39.4%), health literacy (OR = 2.20, bias = 10.0%), and region of origin (not included in the lasso regression model, bias = 9.2%). Clinical characteristics were not significantly associated with the main outcome and had low relative biases (≤ 2.7%). Refusers were more likely to have social vulnerabilities than consenters, but clinical vulnerabilities were similar in both groups. The non-response bias probably occurred in this prison population. Therefore, efforts should be made to reach this vulnerable population, improve participation in research, and ensure a fair and equitable distribution of research benefits.