Theory and practice in medical statistics.
The discipline of statistics generally, and that of medical statistics in particular, has evolved through two traditions, the theoretical and the practical. Their history, traced briefly here, shows recurrent points of contact and a process of gradual merging which is now almost complete. However, the current tendency to build complex mathematical and computing models may lead to over-confidence in their conclusions, when some crucial aspects of the data cannot easily be modelled satisfactorily. Illustrations are drawn from the use of formal stopping rules in the monitoring of clinical trials, and from the treatment of missing data and incomplete compliance with the trial protocol.