Causal thinking in practice: strengths and weaknesses of the clinical vantage point.

The place of causal inference in clinical practice is considered. One function relates to the validation of existing knowledge, as in the evaluation of the medical literature, and is exemplified by the process of editorial selection. A second function relates to the validation of potential knowledge, as in the testing of hypotheses, and is exemplified by the pursuit of a nutritional cause of retarded mental development. Features of clinical practice that contribute strengths or weaknesses to causal inference are then examined. These include the diagnostic process, the effect of cumulative clinical experience, continuity of observation and follow-up, and the focus on disease.