Objectives The main purpose of this study was to demonstrate the relevance of testing indices concerning the psychosocial work environment by item bias or differential item functioning (DIF) analysis. Especially when the work environment for different groups is compared, this kind of construct validation is important. As exogenous variables gender, age, and occupational group were selected.

Methods Data were taken from a cross-sectional study of Danish employees aged 19-59 years (N=5940). The study was carried out in 1990 and followed-up in 1995.

Results Item bias was demonstrated in all indices when analyzed in relation to gender, age, and occupational groups of the total population. Item bias was much weaker or disappeared as the population was divided into main occupational groups and analyzed in relation to the same exogenous variables.

Conclusion For a heterogeneous group of employees, gender, age, and occupational status are significant determinants of the response pattern in relation to indices of the psychosocial work environment. It was concluded that, if the psychosocial work environment for different groups is to be compared, indices should always be tested for item bias in relation to the exogenous variables included in the final analyses. Indices should only be used if there is no item bias. If such indices cannot be constructed, it is suggested that researchers either concentrate on constructing indices that are valid in subgroups or report results based on single-item analyses.

Key terms construct validity; differential item functioning; index; scale