Why “Statistics in Psychiatry”? What makes statistics in psychiatry a particularly interesting intellectual challenge? Why is it not merely a sub-discipline of medical statistics such as the application of statistics in rheumatology or statistics in cardiology? It is in the nature of mental illness and of mental health. Mental illness extends beyond medicine into the realms of the social and behavioural sciences. Similarly, statistics in psychiatry owes as much, or more, to developments in social and behavioural statistics as it does to medical statistics. Statisticians in this area typically user a much wider variety of multivariate statistical methods than do medical statisticians elsewhere.