Is Co-norming Required?

Researchers who have been responsible for developing test batteries have argued that competent practice requires the use of a "fixed battery" that is co-normed. We tested this assumption with three normative systems: co-normed, meta-regressed norms and a system of these two methods. We analyzed two samples: 330 referred patients and 99 undergraduate volunteers. The T scores generated for referred patients using the three systems were highly associated with one another and quite similar in magnitude, with an Overall Test Battery Means (OTBMs) using the co-normed, hybrid, and meta-regressed scores equaled 43.8, 45.0, and 43.9, respectively. For volunteers, the OTBMs equaled 47.4, 47.5, and 47.1, respectively. The correlations amongst these OTBMs across systems were all above .90. Differences among OTBMs across normative systems were small and not clinically meaningful. We conclude that co-norming for competent clinical practice is not necessary.