The Ham D6 is more homogenous and as sensitive as the Ham D17

OBJECTIVE: Using the data of a positive d.b.c.t. comparing an hypericum extract (W55570) to placebo in depressed patients we explored whether the Ham D(6) was unidimentional and in case of a positive answer whether the total score was as sensitive as the total score of the Ham D(17). METHODS: The study was a 6 weeks double blind placebo controlled trial comparing 300 mg of hypericum t.i.d (n=186), to placebo (n=189), in patients with a single or recurrent depression according to DSM-IV. Superiority of hypericum versus placebo on the main outcome criterion (HDRS 17) was already published. The unidimensionality of the Hamilton depression scale 6 and 17 items were tested using a Mokken scale analysis. The effect size according to the initial severity of depression was calculated on the ITT last observation carried forward population. RESULTS: The Ham D(6), covering the core symptoms of depression was unidimensional, implying that improving this score reflects a true antidepressant effect. The Ham D(17) was not unidimensional. Hypericum was an effective antidepressant in patients with a pre-treatment score of 12 or more (n=208) on the Ham D(6), the effect size was 0.46. No difference with placebo was observed for those with a score of less than 12 (n=167). CONCLUSIONS: For the evaluation of an antidepressant effect, because of its specificity and sensitivity, the Ham D(6) should be used as a primary outcome measure rather than the Ham D(17).