On the other hand, all studies in this group had moderate methodological limitations. These limitations arose largely from the simple study designs employed, especially cross-sectional studies where the direction of causality was uncertain. In addition, there was difficulty eliminating the possibility that there had been confounding or co-intervention in some studies.
As well as these internal validity weaknesses, two of the five studies were concerned with Quebec and Ontario legislation from the late 1970s and are therefore not applicable to most or all Canadian provinces now. The remaining three studies were from Norway, so their applicability to a Canadian jurisdiction is presently uncertain.
In sum, there is insufficient evidence in the published, peer-reviewed literature on the effectiveness of mandatory OHSMSs to make recommendations either in favour of or against them.
4.5.3 Evidence for facilitators of and barriers to OHSMS implementation and effectiveness once implemented Within the scope of the review, no evidence was found concerning facilitators and barriers of OHSMS implementation or effectiveness that was of sufficient methodological quality. Little systematic research has been conducted in this area. One study containing quantitative data on this question (Nytro et al., 1998) and three containing qualitative (Chinander, 1998; Lund, 2004; Mitchell, 1998) met the inclusion criteria for the review, but their evidence on facilitators/barriers was judged to be of either Very Low or Low quality (from the perspective of the present review).
4.5.4 Evidence for cost-effectiveness of OHSMS interventions Within the scope of the review, no studies of the cost-effectiveness of OHSMSs or of the cost of OHSMS implementation were found. We are aware of only one study with data on costs (Kjellen, 1997) which was a combined quality, environment and OHS intervention. This study was not included in the review because it arrived after the date for inclusion in the study.
Effectiveness of Occupational Health & Safety Management Systems: A Systematic Review