The prevailing approach to candidate genes creates far more opportunities to produce untrustworthy findings than results that are likely to lead to genuine advances in scientific understanding. This is partly due to insufficient power, which creates the opportunity for false positives due to sampling variation. We return to the issue of power below, where we also provide a recommendation concerning defensible sample sizes. However, there is an additional difficulty with candidate gene studies. An appeal of candidate gene studies is that they are hypothesis-driven. We argue that this is something of an illusion given our current state of knowledge; in reality they are more exploratory than not. It is tempting to think that a particular candidate gene will somehow be different. Yet the history of molecular genetic research provides little evidence to suggest that this is true. Candidate genes are also often justified on the basis of initial findings that fail to hold up to the harsh light of replication. Imagine this hypothetical scenario: A researcher is interested in endophenotype X as an endophenotype for ADHD. Assume that two recent
