Santos et al. BMC Public Health 2011, 11:60 http://www.biomedcentral.com/1471-2458/11/60 Secondary analysis No significant differences between the intervention and control groups were observed in the secondary outcomes (Table 2). The intra-group variations of the SF-36 and WLQ scores showed significant improve- ments in bodily pain scores, general health, vitality, mental health, Physical Component Summary (PCS), and Mental Component Summary (MCS) in the inter- vention group (Table 2). The control group presented statistically significant improvements in bodily pain, social functioning, MCS and output demands (Table 2). In this study, the incidence of WMSD with days away from work was very low during, before and after the study period. In the 10 months prior to the study, dur- ing the three months of the educational program, and in the seven months after completion, there were only four, one and one occurrences, respectively (goodness- of-fit test, P = 0.631). Discussion The present study was designed to compare the effects on QL measured by SF-36, of a specific educational program aimed at preventing WMSD and a program of general health orientation, in workers from a steel trad- ing company. No significant differences in the outcomes were observed between the groups. However, both groups presented with improvements in some physical and emotional aspects. Previous RTC studies evaluating interventions for the prevention of WMSD have yielded inconsistent results. This may be related to differences in the kinds of jobs and tasks, the focus on different WMSDs, differences in the prevention programs, and methodological issues, making comparisons between studies difficult. Ander- sen et al [25], compared the effect of specific exercises training, general exercises, and general health counsel- ing in office workers, and demonstrated reductions in neck and shoulder pain with both types of exercises, but no effect of general health education. In a re- analysis of the same data, the authors observed that asymptomatic individuals at the baseline were more likely to be free of neck-shoulder pain when allocated to the specific training group [26]. Two studies that tested interventions for the prevention of back pain using a back school based education program in the occupational setting (post office) [12,14] and compa- nies involving physically demanding jobs [14] in com- parison to usual care, demonstrated no benefit from a training program. Pillastrini et al compared the effect of an informative brochure (concerning self-care at the work station) and ergonomic intervention with an informative brochure alone for video display terminal users. In the group that received the ergonomic inter- vention there was evidence of lower overload in tasks, Page 6 of 7 and a reduction in lower back, neck, and shoulder symptoms [15]. In the present study, the absence of significant differ- ences between the intervention and control groups may be due to several possible factors. Both groups received educational health orientations and subjects allocated to different groups were working in the same environment, so it is possible that the motivation for the prevention of WMSD also increased in the control group by “con- tamination” from the experimental group. The observa- tion that both groups demonstrated significant improvements in some aspects of the SF36 and WLQ may be related to a placebo effect and/or the fact of being part of a clinical trial ("Hawthorne effect”) [27]. Additionally, the orientation about a health promoting behavior in the control group may have had a beneficial effect on QL. Given that the final evaluation was per- formed at six months, an effect of intervention in the long term cannot be ruled out. In addition, considering that the differences between the intervention and con- trol groups are not clinically or statistically significant (and no consistent numerical trend in favor of one groups was evident), lack of statistical power is not a likely explanation. However, some confidence intervals were wide (some including a difference of 10 points in the variation of scores) and a clinically significant differ- ence between the groups cannot be excluded. Another possible explanation for the absence of a dif- ference in results is the “ceiling effect”, which occurs when the preventing effect is diluted by the good health condition of the sample under study. The company where the study took place had a low incidence of sick- leave, and the mean age and the mean number of years of labor activity in the sample were relatively low. The mean baseline values of all domains of the SF-36 and the WLQ were within the normal range. In addition, baseline values in the control group for the domains of physical functioning (table 1) and bodily pain of the SF- 36 were worse than in the experimental group. Further- more, a negative correlation was observed between the baseline physical functioning score and variation of this score between baseline and week 26 (figure 2). There- fore, subjects with lower baseline scores presented with significantly greater improvements at the 26 week eva- luation. It is possible that the control group was sub- jected to a more intense “regression to the mean” effect, thus reducing differences with the intervention group. Conclusion This study failed to demonstrate a beneficial impact on the quality of life of an educational program aimed to prevent WMSD in comparison with general health edu- cation, in a sample of healthy workers with a low inci- dence of sick-leave. However, both groups demonstrated