British Association for Psychopharmacology Max Hamilton Memorial Lecture Quantitative estimates of drug effects in psychopharmacology: what we measure and what we do not.

This paper is an edited version of the Max Hamilton Memorial Lecture that was delivered at the annual meeting of the British Association for Psychopharmacology in Cambridge in July 1989. In tribute to Professor Hamilton's pioneering efforts in the field, the lecture focuses on several aspects of the measurement process in psychopharmacology. The role of enumeration in the classification of psychopathology is reviewed and its importance illustrated with an example drawn from the literature. Attention is given to the fundamental link between agreements within the field about the nature and qualities of clinical phenomena and the field's ability to construct and use multi-item rating scales to measure meaningful changes in the intensity of psychopathology. The importance of global assessment as a validation procedure is emphasized and selected hazards to reliable inference are examined.