Without a doubt, the two years 1946–8, which I spent under the direction of J.R.N. Stone as a Senior Research Worker in the Department of Applied Economics, Cambridge University, were of central importance to my development as a research scientist. Among the many reasons why I am hopelessly in debt to Stone, one in particular stands out in my mind. It was he who brought Donald Cochrane, then a PhD student at Cambridge University, and me together with all that has meant to me personally and intellectually. For this I have always been and remain extremely grateful.