Developmental ordering, scale types, and strong inference

Developmental ordering, 1 item preceding another in development, is a primary piece of evidence in developmental research. However, testing developmental ordering hypotheses is remarkably difficult; the problem is that researchers rarely have absolute measures (ratio scales). Therefore, directly comparing 2 measures is often not sensible. This article demonstrates that, depending on the type of scale, the observed data pattern is constrained by the underlying relationship. Although the observed data pattern may not reflect the exact relationship, it does limit the possible relationships. Researchers can use this information to reject potential underlying relationships. An application of the method of strong inference (J. R. Platt, 1964) is outlined whereby researchers can use observed data patterns to systematically reject competing developmental ordering hypotheses. The approach requires only standard statistical methods and assumptions.