population. These biases may be small in magnitude, but as we increasingly investigate small associations, their relative importance may be greater than is appreciated.Box 3). In addition, having some baseline data and DNA available on all participants at recruitment into the study at least offers the possibility of investigating the extent to which polygenic scores (and other measured factors at baseline) predict subsequent participation. Without this knowledge, studies in samples with unknown selection/attrition mechanisms run the risk of providing biased and misleading results. In our opinion these important caveats should be borne in mind when interpreting the results of such studies.
