Membership in a specific group can be associated with a degree of health that differs significantly from the general population. Doing a study that focused specifically on joggers, or the employed, or physicians may suffer from membership bias.
Membership bias is a type of selection bias.
This post is part of a series of posts on bias in medical research. You can find the whole bias catalogue here.
Sackett DL. Bias in analytic research. Journal of chronic diseases. 1979; 32(1-2):51-63. PMID: 447779