Small is beautiful – at least when it comes to studies concerning recorded information on a total population. In a small and rather well-organized country like Denmark, one can carry out extensive research on the life circumstances and experiences of an entire citizenry. This is made possible by the existence of Denmark's centralized person register, a computerized database housing a broad spectrum of information on the social circumstances of all inhabitants. Since data are collected and organized by a single national census unit, local or regional variations are no threat to their uniform character. Data concerning the residents of Denmark's biggest cities, as well as of the country's most rural provinces, are collected and recorded using identical methodologies. Danish register data are therefore generally considered to be of a rather high standard.

The crime register, just one of the centralized registers in Denmark, was computerized in 1979. The research project resulting in this book began thirteen years later.

Although previous studies of the criminal career were an extremely important source of inspiration, the quality and availability of the Danish registers were important motivating factors in the present undertaking. Having read many of the international studies on criminal careers, I became convinced that the uniformity of the Danish registers might help to answer questions compromised by the methodological limitations of previous research.