Validation of the problem gambling severity index using confirmatory factor analysis and rasch modelling.

The Problem Gambling Severity Index (PGSI), a screening tool used to measure the severity of gambling problems in general population research, was subjected to confirmatory factor analysis and Rasch modelling to (a) confirm the one-factor structure; (b) assess how well the items measure the continuum of problem gambling severity; (c) identify sources of differential item functioning among relevant subpopulations of gamblers. Analyses were conducted on a nationally representative sample of over 25,000 gamblers compiled by merging data from the Canadian Community Health Survey and Canadian Problem Gambling Index (CPGI) integrated datasets. Results provided support for a one-factor model that was invariant across gender, age, income level, and gambler type. Rasch modelling revealed a well-fitting, unidimensional model with no miss-fitting items. The average severity assessed by the PGSI is consistent with moderately severe problem gambling. The PGSI is therefore weak in assessing low to moderate problem severity, a notable limitation of most brief gambling screens. Evidence of clinically significant differential item functioning was found with only one item, borrowing money to gamble, which behaved differently in gamblers who play electronic gaming machines or casino games compared to gamblers who avoid these games.