Work ability and work functioning: measuring change in individuals recently returned to work

To assess: (1) whether work ability and work-functioning instruments can detect relevant changes in their respective parameters following a return to work (RTW) and (2) what proportion of those returning to work show changes in their work ability and work functioning.

A total of 1073 workers who returned to work after at least 2 weeks of sick leave were invited to fill out three questionnaires in the first 8 weeks after RTW. These consisted of an appraisal of general, physical, and mental/emotional work ability (scores 0-10) and a work-functioning questionnaire (scores 0-100). Minimal Important Change (MIC) was defined to determine the proportion of people, whose scores had changed at weeks 5 and 8 following RTW. The Smallest Detectable Change (SDC) was determined to put the MIC in perspective of measurement error.

Of all participants, 235 were eligible for the analysis. All MIC values were below the SDC and thus not suitable for use. The SDC for work ability was 2.2 and 19.9 for work functioning. In the first 5 weeks after RTW, 10-15% showed a relevant, measurable improvement in work ability, and work functioning based on the SDC margins.

Both instruments were unable to identify change after RTW adequately. We can conclude that 10-15% of individuals showed improvement in work ability and work functioning in the first 5 weeks after RTW when SDC is used.