The effect of part-time sick leave for employees with mental disorders

Part-time sick leave (PTSL) allows employees on full-time sick leave (FTSL) to resume work at reduced hours. When the partly absent employee's health improves, working hours are increased until the employee is able to work regular hours. Studies have found that PTSL is an effective instrument for reducing sick leave durations for employees with musculoskeletal disorders and for employees on sick leave in general. This is the first published article to document how PTSL affects sick leave durations for employees with mental disorders.

The aim is to estimate the effect of PTSL on the duration until returning to regular working hours for employees with mental disorders. We compare this effect to that of PTSL for employees with non-mental disorders ('other disorders').

We use combined survey and register data about 226 employees on long-term sick leave with mental disorders and 638 employees with other disorders. These data contain information about type of disorder, PTSL and FTSL (full-time sick leave) durations, and various background characteristics. We use a mixed proportional hazard regression model that allows us to control for unobserved differences between employees on PTSL and those on FTSL.

Our analyses show that PTSL has no effect on the duration until returning to regular working hours for employees with mental disorders. Furthermore, looking at specific disorders such as depression and stress-related conditions, we find no significant effects of PTSL. In contrast, in line with previous research, we find that PTSL significantly reduces the duration until returning to regular working hours for employees with other disorders. The analyses also illustrate the importance of controlling for unobserved differences between employees on PTSL and those on FTSL. Without this control, PTSL significantly reduces the duration until returning to regular working hours. When we control for unobserved characteristics, this effect decreases, and for employees with mental disorders the effect vanishes entirely.

The lack of an effect of PTSL for employees with mental disorders needs replication in other studies. If subsequent studies confirm our findings, one should not necessarily conclude that PTSL is an ineffective intervention: PTSL may play a role in combination with other workplace interventions and in combination with person-centred interventions. The study is limited by self-reported data about disorders and a relatively small number of employees with mental disorders.

Our findings suggest that while PTSL reduces sick leave durations for employees with other disorders, it does not affect sick leave durations for employees with mental disorders. These results may indicate that PTSL by itself is insufficient for promoting the return to work of employees with mental disorders.

Future studies could benefit from larger data sets with disorder information based on medical assessments. In addition to quantitative effect studies, future studies could focus on qualitative workplace mechanisms that may counteract the potential positive effects of PTSL for employees on sick leave with mental disorders.