The construct validity of the Perceived Stress Scale.
OBJECTIVE
Stress impacts the quality of life and is associated with increased risk of mental and physical disorders. The Perceived Stress Scale (PSS) is widely used for measuring psychological distress. Although the instrument was originally defined as a single construct, several studies based on classical test theory suggest that a two-dimensional structure is more dominant. We aimed to explore the construct validity and dimensionality of the PSS-10 using modern test theory to determine if the scale is predominantly for a one- or a two-dimensional model.


METHODS
The study population consisted of 32,374 citizens who completed the PSS-10 as part of the Danish National Health Survey in 2010. We investigated the construct validity of the PSS-10 by CFA. We examined the scalability by investigating the fit of the data distribution in a unidimensional Rasch model and performing modification of response categories, persons and items. The scale dimensionality was additionally assessed by Mokken and Rasch analysis.


RESULTS
The PSS-10 did not fit the Rasch model. Item four indicated the largest misfit, and items four and seven displayed disordered thresholds. Unidimensionality could not be established although the data showed improved fit to the Rasch model for the two dimensions respectively with the positive and negative items. Mokken analysis revealed fit to the unidimensional model, but disordered thresholds were shown for item four.


CONCLUSIONS
Our large population-based study indicated scalability problems in the current version of the PSS-10. The conducted analysis overall revealed better statistical fit for a two-dimensional than a unidimensional model.
Research Unit for General Practice, Department of Public Health, Aarhus University, Denmark. Electronic address: mm@ph.au.dk.
Marie Germund
MG
Nielsen
Research Clinic for Functional Disorders and Psychosomatics, Aarhus University Hospital, Denmark.
Eva
E
Ørnbøl
Research Unit for General Practice, Department of Public Health, Aarhus University, Denmark; Section for General Medical Practice, Department of Public Health, Aarhus University, Denmark.
Mogens
M
Vestergaard
Psychiatric Research Unit, Psychiatric Centre North Zealand, Copenhagen University Hospital, Denmark.
Per
P
Bech
Public Health and Quality Improvement, Central Denmark Region, Aarhus, Denmark.
Finn Breinholt
FB
Larsen
Public Health and Quality Improvement, Central Denmark Region, Aarhus, Denmark; Department of Psychology, Southern University of Denmark, Odense, Denmark.
Mathias
M
Lasgaard
Research Unit for General Practice, Department of Public Health, Aarhus University, Denmark.
Kaj Sparle
KS
Christensen
D000328:Adult; D000368:Aged; D003718:Denmark; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D011594:Psychometrics / Q000379:methods; D011788:Quality of Life; D015203:Reproducibility of Results; D012107:Research Design; D012938:Social Perception; D013315:Stress, Psychological; D011795:Surveys and Questionnaires / Q000592:standards*
Construct validity; Dimensionality; Perceived Stress Scale; Rasch model; Stress