A systematic review of injury/illness prevention and loss control ...

Length of observationThe length of observation in the studies ranged from two weeks (Greene et al.2005) to 15 years (Mancini et al. 2005). The studies that covered multipleyears were typically the studies evaluating policies or programs and notspecific practices.Years publishedOnly three of the studies were published in the 1980s. The majority of thestudies were published in the 2000s (n=34) with the remaining studiespublished in the 1990s (n=9).Research questionAll but three studies presented some form of a research question. Eachcategory – high, medium and low – had one study that did not state theresearch question.Randomized allocationAll but one of the high quality studies were randomized (eight of nine). Incontrast, the low quality studies only had one randomized study (one of 19).Finally, the medium quality studies had 16 studies that were randomized (16of 44).Recruitment rateThe recruitment rate was not reported consistently. Over two-thirds (67%) ofthe high quality studies reported recruitment rates. Only 36% of the mediumquality studies and fewer than 20% of the low quality studies did. Severalstudies were evaluating regulatory programs and recruitment is not typically aconsideration when evaluating regulations. Several studies were also doneusing employer-level information. The authors did not typically report howmany employers were contacted before permission to conduct the study wasgranted.Covariates and confoundersAll of the high quality studies measured confounders/covariates. Only 70% ofthe medium and less than 5% of the low quality studies accounted forconfounders/covariates. Twelve studies controlled for covariates in the finalanalysis (The breakdown was eight of nine high quality and four of 22medium quality studies.).Statistical analysisThe sophistication of statistical analysis varied across the studies. All thehigh quality studies reported pre-intervention differences between groups and78% adjusted for the pre-intervention differences in their final analysis (n=7).Of the medium quality studies, 91% reported pre-intervention differences24 Institute for Work & Health