title: Evaluating construct validity of the second version of the Copenhagen Psychosocial Questionnaire through analysis of differential item functioning and differential item effect.
abstract: OBJECTIVE
  To evaluate the construct validity of the Copenhagen Psychosocial Questionnaire II (COPSOQ II) by means of tests for differential item functioning (DIF) and differential item effect (DIE).
  
  
  METHODS
  We used a Danish general population postal survey (n = 4,732 with 3,517 wage earners) with a one-year register based follow up for long-term sickness absence. DIF was evaluated against age, gender, education, social class, public/private sector employment, and job type using ordinal logistic regression. DIE was evaluated against job satisfaction and self-rated health (using ordinal logistic regression), against depressive symptoms, burnout, and stress (using multiple linear regression), and against long-term sick leave (using a proportional hazards model). We used a cross-validation approach to counter the risk of significant results due to multiple testing.
  
  
  RESULTS
  Out of 1,052 tests, we found 599 significant instances of DIF/DIE, 69 of which showed both practical and statistical significance across two independent samples. Most DIF occurred for job type (in 20 cases), while we found little DIF for age, gender, education, social class and sector. DIE seemed to pertain to particular items, which showed DIE in the same direction for several outcome variables.
  
  
  CONCLUSIONS
  The results allowed a preliminary identification of items that have a positive impact on construct validity and items that have negative impact on construct validity. These results can be used to develop better shortform measures and to improve the conceptual framework, items and scales of the COPSOQ II.
  
  
  CONCLUSIONS
  We conclude that tests of DIF and DIE are useful for evaluating construct validity.
authors.affiliation: National Research Centre for the Working Environment, Copenhagen, Denmark. jbj@nrcwe.dk
authors.forename: Jakob Bue
authors.initials: JB
authors.lastname: Bjorner
authors.forename: Jan Hyld
authors.initials: JH
authors.lastname: Pejtersen
mesh_terms: D000328:Adult; D003718:Denmark; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007588:Job Satisfaction; D008297:Male; D016272:Occupational Health; D012042:Registries; D015203:Reproducibility of Results; D057566:Self Report; D018582:Sick Leave; D012959:Socioeconomic Factors; D013315:Stress, Psychological / Q000175:diagnosis; D011795:Surveys and Questionnaires / Q000592:standards*; D016526:Workload / Q000523:psychology; D017132:Workplace / Q000523:psychology*