HADS, used in many former studies of the HUNT population [20,29-31], has good reliability and validity compared with other symptom scales of depression and anxiety [10-15]. Several articles have stated its suitability in samples from the general population with the potential to intercept undiagnosed- and untreated cases with depression and/or anxiety [9,11,15]. Such cases may have been missed in previous case-control studies examining the relationship between the Val158Met polymorphism and anxiety and/or mood disorders [3-8,24,25,32,33]. In addition, diagnostic differences also exist, because most previous studies have selected cases according to DSM-IV or ICD-10 categories. However, the use of rigid diagnostic criteria may fail to capture a potential genetic predisposition, and more and more studies have taken this into account by also looking at psychological traits or intermediate phenotypes instead of standard diagnoses [34-36]. HADS based diagnoses of depression and anxiety disorder do not correspond exactly to any of the specific diagnoses of DSM-IV or ICD-10, but HADS includes certain ICD-10 features [11,20]. In particular, HADS-D focuses on anhedonia, by some viewed as a core symptom of depression [14], while the
