This is a project to create unified documentation for individual-level samples of the United States census, covering the years: 1850, 1880, 1900, 1910, 1920, 1940, 1960, 1970, 1980, and 1990. These microdata have proven to be a valuable resource, since they allow researchers to make tabulations tailored to their specific research questions and to overcome incompatibilities in the published census tabulations. In addition, the public use microdata samples have made it possible for researchers to move beyond simple tabular analysis and apply increasingly sophisticated multivariate techniques. This project will enhance the compatibility of variables over time and incorporate the 1850 and 1920 census years into the data series. %%% The public use microdata samples from United States population censuses are of great value in several fields of social science, permitting a variety of researchers to carry out scientific tests of general theories concerning socio-economic trends, migration patterns, social change, and several other aspects of American life. Proper documentation and comparability of variables and coding across samples will increase the value of the data sets for researchers and educators. Already some of these data and codebooks are available over Internet or the World Wide Web, and they will be an important part of the national information infrastructure
