On the Inappropriateness of Using Items to Calculate Total Scale Score Reliability via Coefficient Alpha for Multidimensional Scales

Researchers have the implicit option of calculating internal consistency reliability (coefficient a) for total scale scores derived from multidimensional inventories based on either the inter-item correlation matrix (item unit-level) or the inter-subscale correlation matrix (subscale unit-level). It is demonstrated that item unit-level and subscale unit-level reliability estimates often diverge substantially in practice. Specifically, the item unit-level reliability estimation is often larger than the corresponding subscale unit-level estimate. It is recommended that if researchers calculate total scale score reliability at the item unit-level, then a model-based approach to the estimation of internal consistency reliability (i.e., omega hierarchical) should be applied, when the underlying model is multidimensional. If omega hierarchical cannot be applied for any particular reason, it is recommended that total scale score reliabilities be calculated at the subscale unit-level of analysis, not the item unit-level. © 2013 Hogrefe Publishing.