A number of factors need to be borne in mind when interpreting the above observations. Importantly, none of the definitions of depression in the UK Biobank were obtained from structured clinical interviews with an experienced rater (the gold standard for diagnosing MDD). The closest to that standard in the UK Biobank is the online MHQ17, based on the CIDI-SF18. Our results suggest that self-reported diagnoses using CIDI-SF or other diagnostic questionnaire with full DSM-5 criteria lie on the same genetic liability continuum as MDD. This would argue that MDD cases identified through self-report using a full diagnostic questionnaire will be enriched for more strictly defined forms, with the consequence that results from genetic analysis will include loci that contribute to strictly defined MDD disease risk53,54.
