The relationship between depression and anxiety: construction of a prototypical anxiety and depression scale.

The question of the relationship between anxiety and depression remains to be solved. The fact that clinical pictures show substantial overlap makes it difficult, using conventional instruments, to distinguish between the co-occurrence of anxiety and depression and overlap in definitions and measurement of the two syndromes. This calls for the construction of scales which exclude symptoms common to both syndromes and incorporate symptoms specific only to anxiety or only to depression; i.e. scales with maximum discriminant validity. This article describes the construction of two such scales based on PSE symptoms; a prototypical anxiety scale and a prototypical depression scale. In a sample of 134 non-psychotic psychiatric out-patients these scales show good reliability and validity, both as a measure of severity and as a screening device. Compared to the Hamilton anxiety and depression scales (HARS and HRSD), the correlation between the prototypical anxiety and depression scales is low.