Il genio è la punta estrema del senso pratico.

A Favourite Custom, Lawrence Alma-Tadema, 1909.

The validity of the DSM depression criteria has been questioned. In an examination of comorbidity in twins and the occurrence of future episodes to validate externally the DSM depression criteria, the number of symptoms (the hallmark of the criteria), their duration, and resulting impairment did not predict the presence of depressive illness in a co-twin or future episodes in the proband. Another study found DSM criteria to have poor agreement with core features of melancholia derived from cluster analytic and similar techniques. A consequence of the non-specificity of the diagnostic criteria is seen in prevalence figures for depression which have increased from a population lifetime base rate in the 1960s of about 6–8% to present estimates of over 10% for men and 20% for women. In both periods investigators actively sought and evaluated community samples and used similar methodology, making unlikely the explanations that the increase is based on better identification procedures or a postulated greater willingness of sufferers to seek help. Cohort and period effects (respectively, earlier onset ages for first depression and more new depressions in persons born closer to the present) may account for some of the change, but not to the extent indicated by marked increase in base rates. In another example in a Swedish population cohort study of 2612 persons, the lifetime cumulative probability of suVering from depression was estimated to be almost 27% for men and a staggering 45% for women, but only 8 men and 9 women were identified as having a ‘‘serious’’ depressive illness.