Based on 24 sex-specific relative risk estimates, and using current spousal exposure (or nearest equivalent) as the exposure index, meta-analysis gave an overall estimate of 1.25 (95% confidence interval 1.16-1.36), with no significant heterogeneity.
No characteristics of the index meta-analyses were associated with the potential for overlapping meta-analyses.
After these exclusions, 73 index meta-analyses were eligible (see appendix).
There were 138 overlapping meta-analyses (see appendix), corresponding to 49 (67%) of the 73 index meta-analyses.
Among these 49 topics, the median number of overlapping meta-analyses per topic was two (interquartile range 1-4), including the index meta-analysis.
Using individualized search algorithms for the topic described in each index meta-analysis we searched PubMed for overlapping meta-analyses of randomized controlled trials indexed until February 2013.
Index meta-analyses with and without additional meta-analyses were compared by exact test on the publication venues, types of conditions, types of interventions, and countries of origin.
For fibromyalgia there were also two meta-analyses that considered a wider range of causes of pain (besides fibromyalgia) than the index meta-analysis.
*In some topics not all meta-analyses are overlapping with each other, but they overlap to a lesser or greater degree with the index meta-analysis.
For each index meta-analysis, we extracted information on the intervention(s) tested, the diseases/indications assessed, the number of additional meta-analyses, and whether an author was involved in more than one meta-analysis on the same topic.
For each of the index meta-analyses and the additional ones, we also noted whether it was a Cochrane review and the country of affiliation of the first author, as listed in PubMed.
