The weight of evidence: a method for assessing the strength of evidence on the effectiveness of HIV prevention interventions among young people.

OBJECTIVES: To design a method for assessing the strength of evidence on the effectiveness of different interventions to prevent the spread of HIV that will be the basis for the reviews in this series.

METHODS: The literature on the evaluation of public health interventions was reviewed, and a method was developed in consultation with colleagues involved in this series of reviews and others.

FINDINGS: The method involves the following steps. First, define the key types of intervention that policy-makers need to choose between in the population setting under consideration. Second, define the strength of evidence that would be needed to justify widespread implementation of the intervention. Third, develop explicit inclusion and exclusion criteria for the studies under review. Fourth, critically review all eligible studies and their findings, by intervention type. Fifth, summarize the strength of the evidence on the effectiveness of each type of intervention. Sixth, compare the strength of the evidence provided by the studies against the threshold of evidence that would be needed to recommend widespread implementation. Seventh, from this comparison, derive evidence-based recommendations related to the implementation of each type of intervention in the setting or population group.

CONCLUSIONS: The method proposed here provides a systematic, rigorous and transparent approach to reviewing evidence on the effectiveness of interventions of different types and in different population settings in order to generate recommendations for policy-makers.