We investigated heterogeneity among subgroups based on study quality, study setting, study methodology, and study population. Since there was very high heterogeneity in each subgroup, no meta-analysis by subgroup was performed. Heterogeneity and summary proportions, by subgroup, are presented in the supplement.
One study, reported only in two conference abstracts44,45, was a low-quality report of a spontaneous ADR reporting system in the medical wards of a Nigerian hospital, where 30/2012 (1.5%) patients were reported to have had an ADR-related admission.
The remaining thirteen studies were all conducted as active surveillance studies, eight of which were in adults37-39,41-43,47,49,50,52, four in children36,40,51,53, and one in a mixed adult and paediatric population48. As this latter study presented data for adults and children separately, we could extract separate adult and paediatric datasets from it. Key results from Group 1 studies, grouped by the ADR detection method (spontaneous reporting vs active surveillance) and study population (adults vs children) are presented in Table 3.