Besides advantages, there are several limitations of our study to be noted. In our cross-sectional population sample almost half of the willing participants reported lifetime depression that might introduce sampling bias. Current (BSI) or lifetime depression and current BSI-anxiety were assessed via self-report, with no psychiatric screening that might result inaccurate phenotype calling. However, our data were validated [17,19] in a subsample during face-to-face interviews using the Structured Clinical Interview for DSM-IV (SCID, [20]), the interviewer rated Montgomery Asberg Depression Rating Scale (MADRS, [41]) and the Clinical Anxiety Scale (CAS, [42]). Assessment of recent negative life events and childhood adversities was also based on self-report but again used validated questionnaires as described in the methods section. Our study was cross-sectional thus no longitudinal effects of life stresses were available and therefore persistence of depression and the timing of life events relative to depression onset could not be determined. And finally, because of the limited power further potentially important factors such as social support were not included in the analysis.
