The typical source of information on stocks is a Census. Censuses are periodic counts of all members of a particular population. For example, in the US and in a number of other countries, censuses are taken every 10 years or so. The essential characteristic of a census (which differentiates it from a survey) is that it aims to be complete, it does not involve sampling. In general censuses, every dwelling unit in a population is visited or contacted by census workers. The information collected during censuses necessarily involves data on individual members of households. A household informant is generally asked to list the names, age, gender and ethnicity of other household residents. Because censuses aim to be exhaustive, they generally collect only limited information about each population member. It is indeed difficult to ask more information from each census respondent.