Harmonized Work Health and Safety Laws and Traumatic Occupational Digit Amputation in Australia: A Staggered Difference-in-Differences Study

ObjectiveThis study aimed to determine whether Australia's staggered Work Health and Safety (WHS) harmonization was associated with reduced accepted workers' compensation claims for traumatic occupational digit (finger and thumb) amputation. MethodsThis near-national, administrative claims-based difference-in-differences study covered eight Australian workers' compensation jurisdictions.The primary analysis compared the 2012 and 2013 WHS adoption cohorts with Victoria (never treated) and Western Australia (WA; not yet treated) as comparators.In the pooled model, jurisdictions that had already adopted the laws also served as controls for later adopters.A prespecified exploratory analysis separately evaluated WA's 2022 adoption against Victoria.Claim counts were modeled using Poisson models with jurisdiction and financial-year fixed effects and a log(jobs) offset.Because only six to eight jurisdictions were available, inference relied on exact randomization tests (RI) rather than asymptotic cluster-robust standard errors. ResultsThe analytic sample contained 5,259 primary-outcome claims across 73 jurisdiction-years (the study window recorded 5,502 claims, of which 243 fell within mixed-exposure years excluded by design).The pooled incidence-rate ratio (IRR) was 1.03 (descriptive 95% CI: 0.85-1.25)overall and 1.00 (0.83-1.20) when excluding New South Wales (NSW).Under RI, neither estimate showed evidence of an association (p = 0.89 and p = 0.98, respectively).A naïve pretrend test was significant (p = 0.012), but the corresponding RI test did not detect differential pretrends (p = 0.48).Results were likewise null for machinery-related digit amputation (IRR: 0.99, p = 0.96) and the broader time-loss outcome (IRR: 0.99, p = 0.80).The overall interpretation remained unchanged across sensitivity analyses, including a stacked specification that prevented already-treated jurisdictions from serving as controls. ConclusionsI found no evidence that harmonizing WHS laws was associated with reduced accepted workers' compensation claims for digit amputation among the primary adoption cohorts, but a simulation showed 80% power only for reductions of roughly 40% to 55% or larger.One possible interpretation is that harmonization occurred against an already-declining and already regulated hazard, leaving limited additional room for measurable reductions attributable to the reform.