Categorization plays an integral part in how we see and interpret the world. This is especially true when we attempt to comprehend the complexities of human society, where the heterogeneity of human activity across time and space demands that some criterion (class, gender, age, profession, etc.) be used to reduce the number of variables examined. From the mid-nineteenth century—as statistics evolved from the simple “political arithmetic” of tax collectors and army recruiters into a potential science of human behavior—categorizing the population became a contentious issue that reflected the social and political agendas of data collectors. At the same time, when data refused to be molded to researchers’ assumptions, the task of putting people and their activities into analytical categories challenged the validity of the categories themselves. In this way, statistical representations and categories became socially constructed knowledge.