Abstract
BackgroundThe ‘external validity’ of randomized controlled trials is an important measure of quality, but is often not formally assessed. Trials concerning mass drug administration for helminth control are likely to guide public health policy and careful interpretation of their context is needed. We aimed to determine how representative participants in one such trial were of their community. We explore implications for trial interpretation and resulting public health recommendations.MethodsThe trial assessed was the Entebbe Mother and Baby Study (EMaBS), a trial of anthelminthic treatment during pregnancy and early childhood. In a novel approach for assessing external validity, we conducted a two-stage cluster sample community survey within the trial catchment area and compared characteristics of potentially-eligible community children with characteristics of children participating in the trial.ResultsA total of 173 children aged three to five-years-old were surveyed from 480 households. Of children surveyed, we estimated that mothers of 60% would have been eligible for recruitment, and of these, 31% had actually been enrolled. Children surveyed were compared to 199 trial children in the same age group reviewed at annual trial visits during the same time period. There were significant differences in ethnicity between the trial participants and the community children, and in socioeconomic status, with those in the trial having, on average, more educated parents and higher maternal employment. Trial children were less likely to have barefoot exposure and more likely to use insecticide-treated bed nets. There were no significant differences in numbers of reported illness events over the last year.ConclusionsThe trial had not enrolled all eligible participants, and those enrolled were of higher socioeconomic status, and had lower risk of exposure to the parasitic infections targeted by the trial interventions. It is possible the trial may have underestimated the absolute effects of anthelminthic treatment during pregnancy and early childhood, although the fact that there were no differences in reported incidence of common infectious diseases (one of the primary outcomes of EMaBS) between the two groups provides reassurance. Concurrent community surveys may be an effective way to test the external validity of trials.EMaBS Trial registrationISRCTN32849447, registered 22 July 2005Electronic supplementary materialThe online version of this article (doi:10.1186/1745-6215-15-310) contains supplementary material, which is available to authorized users.
Highlights
The ‘external validity’ of randomized controlled trials is an important measure of quality, but is often not formally assessed
Of the 173 children seen in the community, 104 (60%) had mothers who would have been potentially eligible for recruitment into the trial
We found that Entebbe Mother and Baby Study (EMaBS) trial participants were on average, more likely to have parents with higher levels of education and who were in employment, more likely to come from non-local tribal groups, more likely to sleep under a bed-net and less likely to have barefoot exposure than children in the target population for the trial
Summary
The ‘external validity’ of randomized controlled trials is an important measure of quality, but is often not formally assessed. There have been increasing calls to take into account other factors when assessing the quality of evidence generated by trials [3,4,5,6,7]. These include biological plausibility, reproducibility and external validity [8]. External validity can be considered as the extent to which the results can be generalized to other circumstances Whilst important, these factors may not have received the attention they deserve because their quality is not always easy to assess. The assessment of external validity is important for trials in resource-poor settings, as these may be used to guide wide-ranging public health policy decisions, often in several settings or countries [13,14,15]
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