I thank Dr Murphy for his generous comments on our work with the DST. I fear, though, that he is swimming against the tide with his remarks about the use of the test to validate the diagnosis of melancholia.
The history of medicine tells us that disease entities are recognized by a process of successive approximations. We usually begin with clinical descriptive classifications that are later revised when functional diagnostic indexes become available. Sometimes the clinical categories are narrowed, as in the case of myocardial infarction when ECG criteria and serum enzyme measures were developed. Sometimes the clinical classifications are broadened, as occurred when systematic lupus erythematosus was found to cover a much wider range of severity and chronicity than was thought previously. The point is that functional diagnostic indexes give a new dimension to our understanding of a disease entity; indeed, they usually lead to new definitions of the