Measurement of depressive symptoms in women with breast cancer and women with clinical depression: A differential item functioning analysis

Differential item functioning (DIF) analyses of the Beck Depression Inventory-II (BDI-II) were conducted on samples of 267 women with breast cancer and 294 women with clinical depression. Patterns of items in which there was significant and nonsignificant DIF were identified using statistical tests and measures of DIF effect size. At the most general level, 15 of 21 BDI-II items were associated with nontrivial DIF suggesting that the item responses of these samples do not reflect the same underlying construct. Factor analyses of the BDI-II using a psychometrically defensible method for item level factor analysis supported the conclusions from the DIF analyses. These findings suggest that researchers and practitioners should apply caution when interpreting self-report depression symptoms in breast cancer patients.