Psychometric properties of the Need for Recovery after work scale: test-retest reliability and sensitivity to detect change

Background: Monitoring worker health and evaluating occupational healthcare interventions requires sensitive instruments that are reliable over time. The Need for Recovery scale (NFR), which quantifies workers' difficulties in recovering from work related exertions, may be a relevant instrument in this respect. Objectives: To examine (1) the NFR's test-retest reliability and (2) the NFR's sensitivity to detect the effect of a fatigue inducing change, namely an increase in working hours. Methods: Two year longitudinal data of 526 truck drivers and 144 nurses were used. Two week, one year, and two year test-retest reliability was examined in both stable and unstable work environments by calculating intraclass correlations (ICCs). Work environmental ( in) stability was quantified by four events that might have occurred during the follow up period: (1) a reorganisation or merge (0= yes, 1= no), (2) a change of supervisor or management (0 = yes, 1= no), (3) a change in working hours or work schedules (0 = yes, 1= no), and ( 4) a change in work activities, position, or duties (0 = yes, 1= no). The four scores constituted a work ( in) stability index ranging from 0 to 4. The NFR's sensitivity to detect the effect of the increase in working hours was assessed indirectly by comparing it with an alternative scale, namely the Checklist Individual Strength. Results: Test-retest reliability over a two year interval was good to excellent when applied in stable work environments (ICCs 0.68 to 0.80) but, as expected, poor to fair when applied in unstable work environments (ICCs 0.30 to 0.55). The NFR was sensitive in detecting an increase in work related fatigue due to the increase in working hours (effect size 0.40). Conclusions: The NFR's test-retest reliability and sensitivity to detect change are favourable. This implicates that the NFR may form a valuable part of health surveys and may be a useful tool for evaluating occupational healthcare interventions.