Association between working hours, income, and work-related injury among freelancers in Japan: a cross-sectional study.

Objectives: Limited empirical data are available regarding the safety of self-employed workers in Japan. This study investigated the associations between working hours, income, and work-related injuries among freelancers.

Methods: A cross-sectional study was conducted using data from an internet survey conducted in 2022. Self-employed individuals who did not work as employees or earn an income from their employment were recruited. Work-related injuries, working hours, and annual income were assessed using self-reported questionnaires. Prevalence ratios (PRs) of injury were estimated using modified Poisson regression models, while controlling for covariates. Additionally, PRs were analyzed for each stratum of working hours and income levels.

Results: In total, 1856 freelancers met the eligibility criteria and were included in the study. Among them, 222 (12.0%) experienced at least 1 work-related injury. A significantly higher risk of injury was observed among those working long hours (≥60 h/wk: PR = 1.65; 95% CI, 1.16-2.34; P = .005) and those in the second-lowest income bracket (¥2 to <¥4 million: PR = 1.43; 95% CI, 1.05-1.94; P = .024). Furthermore, several strata exhibited significantly higher PRs, particularly among workers with high incomes who also worked long hours (≥60 h/wk).

Conclusions: Long working hours, particularly exceeding 60 h/wk, are associated with a significantly higher risk of work-related injuries among freelancers. Additionally, 2 high-risk groups were identified based on the combination of working hours and income levels: those with relatively low incomes, and high-income earners who also worked extended hours.