Introduction When evaluating the effectiveness of an intervention it is imperative that one uses the research design with the smallest possible risk of bias (i.e. highest methodological quality).

Methods During this talk I will present a range of study designs that can be used to conduct assessments of intervention effectiveness. These range from the established gold standard for clinical interventions, the randomised controlled trial (RCT), to various non-randomised designs, time-series and case-control studies.

Result It will hopefully become apparent that a lot of the criticism against RCTs being too difficult in occupational health settings is actually often based on misconceptions. At the same time, it is also true that the RCT is not a one size fits all solution, i.e. the only study design that can yield informative results. It is good to understand that there is a gradient from low inherent risk bias methods, such as the RCT, that yield the most reliable results to increasing risk of bias and less reliable results when, for example, one relaxes the demands for removing various sources of confounding.

Discussion Conducting an intervention effectiveness study requires considerable investment in terms of time, money and resources. At worst all this goes to waste by planning, conducting and reporting studies that are either uninformative, unreliable or both.