This book forms part of a project to try to understand the role which the social sciences can play in the formation and evaluation ofpublic policy. It began ten years ago as a result of my own practical experience working as a statistician in British central government, in the Office of Population Censuses and Surveys. This was a most illuminating experience in many ways. It provided a perspective broader than that of academic sociology in universities, in which I had been engaged previously. It gave one a much fuller appreciation of both the advantages and the problems of working with large-scale quantitative data such as the results of the census, population registration and continuous and ad hoc social surveys. And it provided first-hand acquaintance within Whitehall with the problems of bringing social science expertise to bear upon current issues of public policy. In Britain the social sciences have not had an easy passage in the world of government policy-making, and it seemed worth trying to explain why this was so.