The populations described by it will be hopelessly contaminated by members sneaking in the door for financial purposes, or suitable members being left out of it because it would cost the public purse too much if the definition was such that they were let in. The history of the Human Sciences this century has been the move from reductionism and determinism towards more complex and sophisticated models such as General Systems Theory. A causes B . General Systems theory deals with the ideas from different levels, such as biological, psychological, and social. It also incorporates the option of circular relationships, such as positive feedback loops.
Existentialism focuses on the experience and meaning of the person who is suffering the condition.
The nosological systems used in psychiatry have gradually accommodated to these developments. But it certainly irritated the lawyers and the insurance companies. They wanted clear-cut lines, and unambiguous causal relationships. They didn't want the waffle that psychiatrists were spouting in the expert witness stands. Mencken was right.