Deconstructing Therapy Outcome Measurement with Rasch Analysis of a Measure of General Clinical Distress: The SCL-90-R

Rasch analysis was used to illustrate the usefulness of item-level analyses for evaluating a common therapy outcome measure of general clinical distress, the Symptom Checklist-90Revised (SCL-90-R, Derogatis, 1994). Using complementary therapy research samples, we found that the instrument’s 5-point rating scale exceeded clients’ ability to make reliable discriminations and could be improved by collapsing it into a 3-point version (combining scales points 1 with 2 and 3 with 4). This, plus removing three misfitting items, increased person separation from 4.90 to 5.07 and item separation from 7.76 to 8.52 (resulting in alphas of .96 and .99 respectively). Some SCL-90-R subscales had low internal-consistency reliabilities; SCL-90R items can be used to define one factor of general clinical distress that is generally stable across both samples, with two small residual factors.