Covariation of depressive symptoms over time

The covariation over time of depressive symptoms was studied by repeated ratings of the symptoms of individual depressed in-patients. Both within-patient factor analysis of symptom scores and correlation of symptom change scores to total change scores suggested that, while the symptoms of reduced interest and pleasure covaried closely with ratings of observed and reported low mood, the more 'biological' symptoms of sleep and appetite disturbance showed little covariation. The implications for the study of depression are discussed.