Abstraction ability was measured in 67 subjects consisting of depressives, schizophrenics, and normals. Depressives and schizophrenics showed a clear abstraction deficit compared with normals. Schizophrenics had more deficit than the depressives. When degree of depression was correlated with abstraction deficit an important overall relationship was observed. This depression-abstraction deficit relationship did not hold consistently within the three groups (depressives, schizophrenics, and normals) making this finding difficult to interpret.
The need to further characterize a "cognitive profile" of patients along both diagnostic lines and dimensions such as degree of depression is stressed. This has implications for nosology and differential diagnosis. It may lead to indexes by which drug effects can be monitored.
Braff DL, Beck AT. Thinking Disorder in Depression. Arch Gen Psychiatry. 1974;31(4):456–459. doi:10.1001/archpsyc.1974.01760160014004