From the later nineteenth century, a need was recognised for social data that covered a wider range of issues and that were also of more detailed kind than those that could obtained from ‘complete enumerations’ via national population censuses and registration systems. Initially, ‘partial studies’ in the form of monographs as produced by Le Play and his followers – essentially ethnographic case studies -- were seen as the way ahead. But those favouring this approach were unable to solve the problem of how to move from part to whole. Claims of the ‘typicality’ of monographs could never be substantiated. A different approach, that of sample surveys, was proposed by Kiaer, in a shift from typological to population thinking in data collection that paralleled that made by Galton in data analysis. Kiaer’s ‘purposive’ sampling was found to have serious flaws and Bowley, an economist but also an advocate of ‘modern statistical sociology’, proposed and applied the alternative of probabilistic or random sampling. Finally, in the 1930s, Neyman demonstrated the superiority of probabilistic sampling, which was then rapidly taken over by sociologists.