According to interpersonal theories on depression, the type of interaction between depression-prone subjects and their social environment plays a causal role in the development and course of depression (e.g. Coyne et al.). So far, interpersonal theories have been tackled mostly by psychometrical methods. However, non-verbal behaviour plays an important role in human social interactions. It is assumed that 60-65% of human communication is non-verbal. Ethological observations have shown that non-verbal interpersonal behaviour of depressed subjects, as assessed prior to treatment, is related to treatment-response or subsequent course of depression. These results are in line with an interpersonal approach of depression.
