Considers the general classes of measurement error effects recognized by contemporary reliability theory, the consequences of these effects for some descriptive and inferential statistics, and the traditional methodologies used to assess the errors in survey data. Traditional reliability estimation strategies rest on stringent assumptions. This report treats extensions of basic reliability designs to test or correct for violations of these assumptions, including the three-trial model to estimate the effects of true change; variation in the length of time to reinterview to assess test-retest conditioning; multiple trait and multiple item, multiple trial strategies to assess method or condition effects; criterion reliability to estimate net bias; and the degree of covariance between error and the true attribute. 72 pp. Bibliog.