A Differential Item Functioning (DIF) Analysis of the Self-Report Psychopathy Scale

Differential item functioning (DIF) occurs when an item is influenced by a variable irrelevant to the construct of interest. Recent investigations of DIF in the Psychopathy Checklist-Revised (PCL-R) indicated that several PCL-R items demonstrated significant DIF. These findings spurred the current investigation of DIF in a measure of subclinical psychopathy closely tied to the PCL-R, namely a 40-item version of the Self-Report Psychopathy Scale (SRP). Participants (N = 383) completed the 40-item measure and we investigated these items for DIF across genders and ethnicities. Results indicated that the majority of SRP items were free of DIF. Only two items demonstrated significant DIF, one between genders and the other between ethnicities. Given the paucity of SRP items with DIF – only 5% – such a finding may have been obtained by chance. In turn, we do not recommend dropping or modifying these items. Rather, our results suggest that users of the SRP should feel confident that its items function equivalently across genders and ethnicities. Future studies of differential test functioning (DTF)