Assessment of generalisability in trials of health interventions: suggested framework and systematic review

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Abstract
Can the intervention be delivered elsewhere? Several factors affect whether an intervention can be delivered and received in other sites. Firstly, an intervention must be feasible. Providers will vary in their capacity to implement an intervention,w3 as will institutions in being suitable places for an intervention.w4 The presence of local “champions” may influence feasibility in a particular site.4 Some interventions require the existence of other health services4—for example, services for treating sexually transmitted infections require microbiology laboratories to target the right patients. Interventions may also require adequacy in other sectors such as transport. Feasibility has a cost dimension: an unaffordable intervention lacks general feasibility. Secondly, an intervention must achieve adequate coverage. This may depend on the overall comprehensiveness of health systems or on whether providers can reach people in other ways—for example, through outreach. Adequate coverage may be more difficult in some sites or sub-populations. Finally, an intervention generally must be acceptable to be effective. Acceptability refers to participants' assessment of their experience of an intervention and will influence whether recipients adhere to treatment plans, act on health advice, or return for follow-up.4 For example, condom promotion has proved acceptable and subsequently effective in urban Tanzania but not in rural regions.w5 Acceptability will vary between populations as it depends on cultural norms and can have economic dimensions. For example, HIV voluntary counselling and testing services that require clients to attend clinics twice (first for testing and then for results) may be acceptable in high income settings but not low income settings because transport or opportunity costs are too great.w3 Factors relating to delivery of an intervention are best documented by embedding an evaluation of process in trials.5 The study collects quantitative and qualitative data on planning, delivery, and uptake and how context affects them.