Measurement invariance of the General Health Questionnaire GHQ 12-item version (GHQ-12): A large UK longitudinal study across students and non-students

Understanding how levels, patterns, predictors, and outcomes of mental health issues differs in students relative to non-students can inform more effective and better tailored prevention and intervention for mental health in higher education contexts. However, comparisons of mental health in student and non-student groups depend on the critical but seldom-tested assumption of measurement invariance. In this study, we use data from the UK household longitudinal study (UKLS) to evaluate the measurement invariance of the scores from a commonly used mental health measure: the General Health Questionnaire 12-item version (GHQ-12) across students and non-students. Using a bifactor model to take account of wording factors we found measurement invariance up to the scalar level for students and non-student groups. This provides support for the use of instruments for comparing mental health issue levels and candidate risk factors and outcomes across students and non-students.