Introduction to the special section: Measurement equivalence in child development research

Debates among developmental scientists regarding the meaning of a set of empirical findings often revolve around the idea that the basic nature of the underlying construct may be different across developmental states or demographic groups. These debates demand greater consideration of the operational definition of underlying constructs at different developmental states or among subsets of the population. Furthermore, the analytical techniques used in the research involved in these debates generally presuppose the equivalence of measures across developmental states or groups. The purpose of this article is to describe why developmental researchers should be concerned with measurement issues, including item equivalence, functional and scalar equivalence, and equivalence of translated assessments. This article and the four subsequent articles that make up the Special Section of this issue of Child Development Perspectives provide " best practice" guidance for examining invariance and equivalence of measures across developmental changes, across age groups, and across groups who differ in participant characteristics.