RESUMEN
An intervention's effectiveness is judged by whether it produces positive outcomes for participants, with the randomized experiment being the gold standard for determining intervention effects. However, the intervention-as-implemented in an experiment frequently differs from the intervention-as-designed, making it unclear whether unfavorable results are due to an ineffective intervention model or the failure to implement the model fully. It is therefore vital to accurately and systematically assess intervention fidelity and, where possible, incorporate fidelity data in the analysis of outcomes. This paper elaborates a five-step procedure for systematically assessing intervention fidelity in the context of randomized controlled trials (RCTs), describes the advantages of assessing fidelity with this approach, and uses examples to illustrate how this procedure can be applied.