Rasch model of the GAIN Substance Problem Scale among Canadian adults seeking residential and outpatient addiction treatment

The analysis broadly supports use of the SPS as an additive measure of global substance severity in men and women and both residential and outpatient settings. Although DIF was not a major concern, there was evidence of item redundancy and suboptimal matching between items and persons. Findings highlight potential opportunities for further improving this scale in future research and clinical applications of the GAIN.