Comparison of self-reported and public registered absenteeism among people on long-term sick leave due to musculoskeletal disorders: criterion validity of the iMTA Productivity Cost Questionnaire

OBJECTIVE: To evaluate criterion validity of the iMTA Productivity Cost Questionnaire (iPCQ) by comparing iPCQ-reported occurrence and duration of long-term absenteeism (> 4 weeks) with public registry data collected from the Norwegian Labour and Welfare Administration (NAV) among people on sick leave due to musculoskeletal disorders. METHOD: Baseline data from a cohort study was used, in which people on sick leave for at least 4 weeks due to musculoskeletal disorders were recruited electronically through the NAV website. To compare the occurrence of long-term absenteeism overall agreement between the two methods was measured by percentages. To compare the duration (number of days with absenteeism) and adjusted duration (number of days with complete absenteeism) of long-term absenteeism we conducted intraclass correlation coefficient (ICC) two-way random average agreement, descriptive statistic and Wilcoxon signed-rank test. RESULTS: In total, 144 participants with a median age (range) of 49 (24–67) were included. The overall agreement on the occurrence of long-term absenteeism was 100%. The ICC value was 0.97 and 0.86 for duration and adjusted duration of long-term absenteeism, respectively. The median difference((iPCQ-registry)) between the two methods was 0 and 17 days for long-term absenteeism duration and adjusted duration, respectively. A significant difference between the two methods was observed (Wilcoxon signed-rank test, p < 0.001) with regards to adjusted duration of long-term absenteeism. CONCLUSION: The iPCQ showed good agreement with public registry data regarding the occurrence and duration of long-term absenteeism among people with musculoskeletal disorders on long-term sick-leave in Norway. However, the iPCQ does not cover part-time sick-leave and thereby potentially overestimate the total amount of long-term absenteeism. TRIAL REGISTRATION: ClinicalTrials.gov Identifier no. NCT04196634.