Estimation of equable scale scores and treatment outcomes from patient-and clinician-reported PTSD measures using item response theory calibration

Across multiple RCTs, discrepancies between patient and clinician reports of PTSD symptoms are at least a partial contributing factor to large discrepancies between treatment outcome effect sizes from self-report and clinician reports within the same patients. Using secondary data from the NIDA-funded Women and Trauma Study, we demonstrated Common Persons Item Response Theory (IRT) Calibration for calibrating self-reported and clinician-reported PTSD severity scores in a manner similar to the process used to produce equated scores across multiple forms of standardized tests (e.g., SAT, GRE). Under IRT calibration, treatment effect sizes between the CAPS and MPSS-SR did not differ, while with the noncalibrated measures, the CAPS effect size was 85% larger than the MPSS-SR. Further, across the range of a combined CAPS/MPSS-SR gold standard, IRT-calibrated CAPS and MPSS-SR individual scores did not differ; for uncalibrated individual scores, MPSS scores were higher than CAPS scores at higher levels of PTSD severity while the reverse was true at lower levels of severity. The use of IRT calibration approaches for calibrating self-report and clinical interview measures of PTSD will allow treatment researchers to reflect the treatment effect on PTSD as a construct (regardless of reporter) as opposed to being limited to reporting treatment effects that may be discrepant within patients and specific to the particular assessment measure being employed.