Measurement invariance of the SQWLi instrument over time

The SQWLi questionnaire was developed for the long-term measurement of subjectively perceived quality of working life. The aim of this study is to test the instrument's measurement invariance between 2009 and 2019 and determine whether - despite the modifications made to the instrument over the years - the results remain comparable. Data from eight representative surveys of the economically active population in the Czech Republic were analysed (total N = 6909) using the MG CFA method (configural, metric, and scalar invariance) and the alignment method (approximate measurement invariance). The findings from the MG CFA tests for measurement invariance indicate that the SQWLi instrument achieves configural and metric invariance over time but not full scalar invariance. Achieving a partial scalar invariance would be challenging because of the many high modification indices; therefore, an approximate measurement invariance approach, namely the Alignment Method, was applied. The results suggest that comparisons of latent means across all years can be made. Consequently, it is possible to make meaningful comparisons of overall indices of dimensions (batteries) and of more general domains. However, not all the individual items can be compared. The results confirm that the biggest risk of invariance is caused by conceptual changes to items and by substantial or frequent modifications to item wording. Conversely, the results also show that a conceptual change to an entire dimension may not necessarily cause any problem on the general level, and that a disruption of invariance caused by changes to the range of scales used can be rectified by means of their harmonisation ex post.