Psychometric properties of the 28-item General Health Scale (GHQ-28). Analysis from the Classical Test and Item Response Theories in Ecuadorian university students

Background: Monitoring mental health in the university population is essential to be able to meet the demands and needs of this segment. For this, it is essential to have properly calibrated instruments to adequately describe reality and generate adequate decision making. Aim: Confirm bi-factor model and measurement invariance by gender of the 28-item General Health Questionnaire (GHQ- 28) in university students in Ecuador according to Classical Test Theory (CTT). In addition, analyze the discrimination parameters, item difficulty and global reliability according to the Item Response Theory (IRT). Participants and procedure: A descriptive and instrumental design of the GHQ-28 from a bi-factor model was used with 476 participants, of whom 61.5% were women and 38.5% men, aged 17 to 47 years (M = 21.2; SD = 3.7), from 34 higher education centers in Ecuador. Results: The factorial validity of the GHQ-28 was confirmed based on a bi-factor model. In addition, it showed measurement invariance across gender of the participants according to the CTT. The items of the scale present adequate discrimination and difficulty, and the global reliability of the measure is correct based on IRT. Conclusions: The GHQ-28 is a valid test that can be applied to a university population in Ecuador. The scale is essentially unidimensional in its assessment of psychological distress and the contribution of the IRT broadens and complements the information on the known items of the scale previously collected by the CTT.