Sampling Variability of Performance Assessments

In this article, performance assessments are cast within a sampling framework. More specifically, a performance assessment is viewed as a sample of student performance drawn from a complex universe defined by a combination of all possible tasks, occasions, raters, and measurement methods. Using generalizability theory, we present evidence bearing on the generalizability and convergent validity of performance assessments sampled from a range of measurement facets and measurement methods. Results at both the individual and school level indicate that task-sampling variability is the major source of measurement error. Large numbers of tasks are needed to get a reliable measure of mathematics and science achievement at the elementary level. With respect to convergent validity, results suggest that methods do not converge. Students' performance scores, then, are dependent on both the task and method sampled.