The reliability and validity of measurement is analyzed by a sampling model based on generalizability theory. A model for the relationship between a measurement procedure and an attribute is developed from an analysis of how measurements are used and interpreted in science. The model provides a basis for analyzing the concept of an error of measurement, the distinction between random errors and systematic errors, standardization of measurement procedures, the distinction between reliability and validity, and an analysis of convergent and discriminant validity. Within the sampling model, the concepts of reliability, validity, and import arise naturally as necessary requirements for the results of measurement to be meaningful. This model also provides a basis for examining the relationship between measurement and theory, and reviews some general techniques for developing theory and controlling errors of measurement. (Author/CP)