The production of studies regarding the evaluation of the effectiveness of preventive interventions is still modest, especially in comparison with the production of effectiveness studies in the clinical field. This can be at least partly due to the real difficulty to evaluate the effects of preventive actions on injuries at work and on occupational diseases, which can be affected by many other causal factors, including regulatory actions, periods of economic and employment crisis, technological innovations, changes in the distribution of risk factors in the population.

Such complexity must be carefully considered when the researcher approaches the effectiveness evaluation in the occupational health field and, to do so, the evaluation of effectiveness should be planned before to start with the intervention.

Three elements have to be clearly defined:

1. the objective of the assessment;

2. the intervention that the researcher wants to evaluate; and

3. the outcome to be measured as effect of the intervention itself.

At the same time, it should be ensured whether the considered preventive intervention has already been studied. This could be performed searching the literature, in order to find the information relevant to the problem that needs to be addressed.

Finally, before promoting the intervention – on the basis of technical knowledge and availability of the tools, considering also economical and time concerns – it is necessary to choose the type of study design that is more appropriate and feasible to assess the effectiveness of the intervention: it has to be considered the growing evidence coming from studies like case-report, cross-sectional, before-after, controlled before-after, interrupted time series, case-control, cohort and randomised (individually or by cluster) controlled trials.