Objective In 2015, South Australia replaced its workers’ compensation system with the aim of improving return to work rates. We examined whether this was achieved by focusing on the duration of time off work, as well as claim processing times and claim volumes to understand how this may have been achieved.

Methods The primary outcome was mean weeks of compensated disability duration. Secondary outcomes tested alternative mechanisms of a change in disability duration: (1) mean employer report and insurer decision times to evaluate whether there had been changes in claim processing and (2) claim volumes to determine whether the new system altered the cohort under investigation. Outcomes were aggregated into monthly units and analysed with an interrupted time series design. Three condition subgroups—injury, disease and mental health—were compared in separate analyses.

Results While disability duration steadily declined before the RTW Act came into effect, afterwards it flatlined. A similar effect was observed in insurer decision time. Claim volumes gradually increased. Employer report time gradually decreased. Condition subgroups mostly followed a similar pattern to overall claims, though the increase in insurer decision time appears largely driven by changes in injury claims.

Conclusions The increase in disability duration after the RTW Act took effect may be attributable to an increase in insurer decision time, which itself could be due to the disruption of overhauling a compensation system or the elimination of provisional liability entitlements that incentivised early decision making and provided early intervention.