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

doi:10.1136/bmj.333.7563.346

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C Bonell, senior lecturer (chris.bonell@lshtm.ac.uk)1,
A Oakley, professor2,
J Hargreaves, lecturer1,
V Strange, research officer2,
R Rees, research officer2

¹ London School of Hygiene and Tropical Medicine, London WC1E 7HT
² Social Science Research Unit, Institute of Education, University of London, London

Correspondence to: C Bonell

Accepted 19 May 2006

Most evaluations of new treatments use highly selected populations, making it difficult to decide whether they would work elsewhere. Systematic evaluation and reporting of applicability is required

Randomised trials of health interventions generally describe outcomes among participants with little consideration of whether the effects can be generalised. However, generalisability cannot be assumed with either biomedical interventions or more complex social interventions.^w1 If their results are to be translatable into policy and practice decisions, trials must provide evidence about how relevant the interventions might be to other sites and populations.1 ^w2 Such information is particularly crucial for resource poor settings.2

Although CONSORT criteria for reporting randomised trials include assessment of generalisability,3 a framework for empirically assessing and reporting this is lacking. We consider the factors affecting generalisability using examples from HIV and sexual health, examine how a sample of trials looked at generalisability, and suggest how to improve evaluation.

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 …