In most European countries, regular censuses of population together with vital registration allow the historical geography of population changes to be studied with some confidence for the nineteenth and twentieth centuries. For earlier periods, we must rely in the main upon parish registers. Henry showed that these records of vital events could be used to build up pictures of families allowing many demographic measures to be calculated. Most English registers do not include as much information as the French registers used by Henry. They rarely give the ages of bride and groom at marriage and thus both bride and groom must be linked to their baptism records for the age at marriage to be calculated. On the other hand, whereas French registers begin in the early seventeenth century, many English registers were kept almost continuously from the mid sixteenth century. Wrigley and Laslett set up the Cambridge Group for the History of Population and Social Structure in large part to replicate in England the pioneering work in French historical demography completed by Henry. Based on a study of the parish of Colyton in Devon, Wrigley showed that English registers could be used for family reconstitution studies. As Levine remembers, Wrigley’s “Colyton study revealed that a new kind of history—a people’s history—could result from counting vital events”. Through radio programmes Laslett appealed to local historians to make counts of the monthly totals of vital events in Anglican baptism, burial and marriage registers so that the Group could make a selection of a few dozen reliably registered parishes for reconstruction. By 1974, 530 tabulations had been received. Of these, 404 covered the core period chosen (1661–1812), were tolerably continuous over this period and were accurately tabulated.