Bibliometric study of ‘overviews of systematic reviews’: evaluation of prevalence, citation and impact factor
Abstract Background: Overviews synthesizing the results of multiple systematic reviews help inform evidence-based clinical practice. In this first of two companion papers, we evaluate the bibliometrics of ‘overviews of systematic reviews’, including their prevalence, number of citations, and factors affecting citation rates and journal impact factor.Methods: We searched MEDLINE, Epistemonikos and the Cochrane library databases. We applied eligibility criteria to identify overviews that: (a) aimed to focus on synthesizing reviews, (b) conducted a systematic search, (c) had a full methods section, and (d) examined a health intervention or clinical treatment effect. A multivariate regression was conducted to determine the association between citation density and impact factor and 6 predictor variables of interest. Results: We found 1218 overviews published from 2000 to 2020; the majority (73%) of which were published in the most recent 5-year period (2016-2020). We extracted a selection of these overviews (n=541; 44%) dated from 2000 to 2018. The 541 overviews were published in 307 journals; the Cochrane Database of Systematic Reviews (8%), PLOS ONE (3%) and the Sao Paulo Medical Journal (2%) being the most prevalent. The majority of overviews (70%) were published in journals with impact factors between 0.05 and 3.97. The average citation rate was 90 (SD ±219.7) over 9 years, or 10 citations per overview per year. In multivariate analysis, overviews with a high number of citations and high journal impact factors tended to have more authors, larger sample sizes, be open access and report funding source. Conclusions: We found an 8 fold increase in the number of overviews from 2009 to 2020; and a representation of one published a day in 2020. Factors driving the increase in overviews include the exponential increase in the number of systematic reviews, the publication of Cochrane guidance on overview of reviews in 2009 and the subsequent publication of the first Cochrane overview in the same year. Our study found a significantly higher mean citation count of 10 overviews per year, published in journals with a mean impact factor of 4.4. These data indicate that, overall, overviews perform above average for the journals in which they publish. We also found that highly cited overviews in high impact factor journals had group authorship, large sample sizes, were openly accessible, and reported funding source.