Does having a certified occupational health and safety management system lead to a greater injury rate reduction? An evaluation of the Certificate of Recognition program in Ontario, Canada

• Construction firms that achieve a certified OHSMS experience greater injury rate reductions than similar non-certified firms. • The effectiveness of certification was smaller and less precise in earlier years with no effects in small firms and non-construction firms. • OHSMS program evaluations can inform decision-makers on when, and under what circumstances programs work and where improvements can be made. Introduction: Occupational health and safety management system (OHSMS) programs are designed to create safer workplaces. However, research on their effectiveness is limited in terms of representation and rigor. This study evaluates whether firms that obtained an OHSMS certification via the Certificate of Recognition (COR) program experienced greater injury rate reductions than similar non-certified firms in Ontario, Canada. Method: Using firm and claim-level data from the Workplace Safety and Insurance Board and COR registration data from the Infrastructure Health and Safety Association, the effect of becoming certified on firm-level injury rates was assessed using a matched difference-in-differences study design with population averaged negative binomial regression models. Results: A total of 346 certified firms were matched with 310 non-certified firms during the years 2009 to 2020. Firms that became certified were associated with a greater reduction in the lost time injury rate (incidence rate ratio (IRR): 0.72; 95% confidence interval (CI): 0.63–0.84), high-impact injury rate (IRR: 0.80, 95% CI: 0.66–0.97) and no reduction in the no lost time injury rate (IRR: 1.00, 95% CI: 0.92–1.08) relative to the change in similar non-certified firms. The effectiveness of certification was strongest in firms that were recently certified, larger, and in the construction sector. Conclusions: The findings suggest that COR can be an effective program in reducing injury rates in construction firms, and among larger and more recently certified firms. It is less effective in smaller and earlier certified firms, and not effective in non-construction firms. Furthermore, the effectiveness in construction firms may be subject to unmeasured selection bias. Practical Applications: OHSMS program evaluations can inform decision-makers on when, and under what circumstances programs work and where improvements can be made. In particular, the COR program appears most effective for large construction firms whereas small construction firms may benefit from other tools.