This talk examines the potential lack of measurement invariance across groups in the Professional Identity Scale in Counseling (PISC; Woo & Henfield, 2015). Invariance suggests consistent response patterns across groups, facilitating valid score comparisons. However, if the PISC elicits systematically different responses among groups, comparisons become invalid due to underlying response mechanism variations. Understanding such nuances is crucial for ensuring the reliability and validity of assessment tools in counseling research.