Covariance structure modelling is applied to the problem of estimating reliability and measurement error in survey data. To provide a basis for grouping certain question or variable types (data from questions), a simple typology based on the formal characteristics of the questions is outlined. From this classification, models for the different question types are used to estimate reliability and method influences on the observed responses. Differential reliability across questions within each question type is investigated in terms of a subsidiary hypothesis that the degree of reliability varies systematically according to the substantive context of a question. Estimates of measurement error are employed to disattenuate a correlation matrix and thereby demonstrate the differences obtained from correlation and regression analyses when these issues are ignored. (Author/CM)