Abstract: We located 23 studies: two RCTs with 1414 workplaces, two CBAs with 9903 workplaces, one ITS with six outcome measurements, 12 panel studies and six qualitative studies with 310 participants. Studies evaluated the effects of inspections in general and the effects of their consequences, such as penalties. Studies on the effects of prosecution, warnings or closure were not available or were of such quality that we could not include their results. The effect was measured on injury rates, on exposure to physical workload and on compliance with regulation, with a follow-up varying from one to four years. All studies had serious limitations and therefore the quality of the evidence was low to very low. The injury rates in the control groups varied across studies from 1 to 23 injuries per 100 person-years and compliance rates varied from 40% to 75% being compliant. The effects of inspections were inconsistent in seven studies: injury rates decreased or stayed at a similar level compared to no intervention at short and medium-term follow-up. In studies that found a decrease the effect was small with a 10% decrease of the injury rate. At long-term follow-up, in one study there was a significant decrease of 23% (95% confidence interval 8% to 23%) in injury rates and in another study a substantial decrease in accident rates, both compared to no intervention. First inspections, follow-up inspections, complaint and accident inspections resulted in higher compliance rates compared to the average effect of any other type of inspections. In small firms, inspections with citations or with more penalties could result in fewer injuries or more compliance in the short term but not in the medium term. Longer inspections and more frequent inspections probably do not result in more compliance. In two studies, there was no adverse effect of inspections on firm survival, employment or sales. Qualitative studies show that there is support for enforcement among workers. However, workers doubt if the inspections are effective because inspections are rare and violations can be temporarily fixed to mislead inspectors. There is evidence that inspections decrease injuries in the long term but not in the short term. The magnitude of the effect is uncertain. There are no studies that used chemical or physical exposures as outcome. Specific, focused inspections could have larger effects than inspections in general. The effect of fines and penalties is uncertain. The quality of the evidence is low to very low and therefore these conclusions are tentative and can be easily changed by better future studies. There is an urgent need for better designed evaluations, such as pragmatic randomised trials, to establish the effects of existing and novel enforcement methods, especially on exposure and disorders.

Plain-language summary: We found 23 studies. Two studies were randomised controlled trials with 1414 workplaces. Fifteen non-randomised studies analysed injury rates of firms obtained from large administrative databases. Six studies with more than 340 participants in total reported on the opinions of workers or employers. Two studies randomly allocated inspections or no inspections to workplaces. After one year follow-up the non-fatal injury rate in one study and the frequency of physical overload in the other study were still similar in both study groups. Another five similar but lower quality studies had inconsistent results at short and medium-term follow-up. Two other non-randomised studies found that after more than three years inspections decreased injuries and accidents by 23% compared to no inspections and there was no effect on the firms' productivity. Specific inspections resulted in higher compliance rates. Inspections with penalties could result in fewer injuries and more compliance in the short term in small firms. Longer inspections and more frequent inspections probably do not result in more compliance. Two studies did not find a harmful effect of inspections on firm lifetime or employment. Qualitative studies showed that there is support for enforcement among workers. However, workers doubt if inspections are effective because they are rare and violations can be temporarily fixed to mislead the inspectors. We concluded that inspections decrease injuries in the long term but probably not in the short term. The evidence is of low to very low quality because the results across studies are inconsistent and studies are observational and do not take into account other factors that could affect the results. In addition, the magnitude of the effect is uncertain because it varies from a 3 to 23 per cent decrease in injury rates. Because the quality of the evidence is low, future studies can easily change our conclusions. There is an urgent need for large-scale randomised trials to evaluate different types of inspection methods on exposure, disorders and injuries.