The Perceived Stress Scale is essentially unidimensional: Complementary evidence from ancillary bifactor indices and Mokken analysis

Stress is a significant contributor to physical and mental health. However, there is considerable variability in response to stress, underscoring the role of stress perception in health outcomes. Perceptions of stress are influenced by socio-demographic and cultural factors. The Perceived Stress Scale (PSS) has been used extensively to assess stress among different populations and for cross-cultural comparisons. Given its wide-ranging application, the rigorous assessment of its psychometric properties is necessary to solidify its standing as a dependable measure. The scale was originally conceptualized as unidimensional but there has been controversy regarding its factor structure, leading to various factor models. Conclusions about the structure of the PSS were largely based on fit indices in confirmatory factor analysis and often did not go beyond fit indices. In addition, classical test theory indices are sample dependent and it is not surprising that instruments can exhibit different properties in different samples. Over reliance on fit indices can lead to overly simplistic interpretations of underlying dimensionality. Hence, the current study extends this research by using item response theory and examining ancillary bifactor indices to determine the amount of variance explained by the total scale and subscales. Participants were students (n = 322) at a South African institution who completed the PSS and a demographic questionnaire. Fit indices in confirmatory factor analysis indicated that a one-factor model, a bifactor model and a correlated-two factor model fit the data to an acceptable degree (GFI > 0.95, CFI > 0.90, RMSEA