V. DESIGN-BASED APPROACHES FOR IMPROVING MEASUREMENT IN DEVELOPMENTAL SCIENCE.

The study of change and variation within individuals, and the relative comparison of changes across individuals, relies on the assumption that observed measurements reflect true change in the construct being measured. Measurement properties that change over time, contexts, or people pose a fundamental threat to validity and lead to ambiguous conclusions about change and variation. We highlight such measurement issues from a within-person perspective and discuss the merits of measurement-intensive research designs for improving precision of both within-person and between-person analysis. In general, intensive measurement designs, potentially embedded within long-term longitudinal studies, provide developmental researchers an opportunity to more optimally capture within-person change and variation as well as provide a basis to understand changes in dynamic processes and determinants of these changes over time.