In 1871, Maudsley presented a paper entitled ‘Is Insanity on the Increase?’ (Maudsley, 1872). Over 100 years later, Der published a paper entitled ‘Is Schizophrenia disappearing?’ (Der et al, 1990). Investigations of time trends in schizophrenia encompass centuries of disease reports and records, and generations of research. In this chapter, we will examine the evidence for secular trends in the incidence and outcome of schizophrenia.
Time trends are of sustained research interest because they address a basic question: Are things getting better or worse? A quantitative answer to this question is central to health services planning: it provides a means to anticipate the future, and a means to judge past efforts. The analysis of time trends has yet another purpose. Examining secular trends may also contribute to our understanding of the nature and the determinants of disease. In seeking to describe temporal variations in a population's disease experience, we may obtain the first glimpse of factors influencing the occurrence and shaping the outcome of disorders. An underlying shift in the human gene pool can only occur over a great deal of time; in contrast, changes in the social, biological and physical environment may occur over a shorter span of time. These environmental influences are potentially reflected in variation in rates of disease over years and decades.