Evidence of undercounting: Collecting data on mental illness in Germany (c. 1825-1925).

Collecting data about people with mental disorders living outside of asylums became a heightened concern from the early nineteenth century onwards. In Germany, so-called "insanity counts" targeted the number and sometimes the type the mentally ill who were living unattended and untreated by professional care throughout the country. An eagerly expressed assumption that the "true" extent of the gathered numbers must be much higher than the surveys could reveal came hand in glove with the emerging task of "managing" insanity and its potential dangers in a modern society. The doorstep of the family home became a crucial site in psychiatrists' and enumerators' efforts to register the most sensitive of personal data. This article traces the ever more diligent methods that were employed to obtain the desired information, as well as the hidden agenda of the postulate of missing data itself. It also addresses the profound impact that the presumption of having only incomplete data has had on the practice of counting and surveying, as well as on the understanding of the need for professional monitoring of mental illness.