A methodological analysis of developmental studies of identity conservation and equivalence conservation

Reviews the discrepant findings which have been reported during recent years on the order of emergence of identity conservation and equivalence conservation. An analysis of the procedural details of the conflicting studies revealed that the discrepant findings are probably the result of a measurement error (judgments-plus-explanations response criteria) and a sampling error (older S samples) routinely committed in studies reporting that identity and equivalence do not emerge in a fixed order. Some new data from preschool, kindergarten, and 3rd-grade Ss in an experiment in which these 2 errors were controlled provide support for this conclusion. The general consequences of measurement and sampling errors for concept development studies are discussed. (37 ref)