A 2025 bibliometric analysis published in the Journal of Multidisciplinary Healthcare gives the first systematic look at a practice methodologists have long worried about anecdotally: systematic reviews and meta-analyses written by a single author. Screening 292,323 Scopus-indexed articles published between 2000 and 2023, the study (Shamsi et al., 2025) identified 2,504 single-author systematic reviews and meta-analyses and found their numbers climbing steadily — an earlier trend estimate the same paper cites put the annual growth rate at roughly 6.5% between 2000 and 2020. The finding sits awkwardly next to decades of methodological guidance, from the Cochrane Handbook to PRISMA 2020, that treats independent screening and selection by two or more reviewers as close to a baseline requirement for a credible review.
What the bibliometric data actually shows
The Shamsi et al. analysis is deliberately narrow and empirical: it counts single-author systematic reviews and meta-analyses in Scopus and checks how they sit against evidence-based-medicine guidance, rather than surveying opinion. Two findings stand out for a research-administration audience. First, the practice is not confined to low-profile venues — the authors found single-author reviews published in Q1-ranked journals, and noted that a meaningful share of repeat single authors published that way more than once, often in the same journal, pointing at inconsistent editorial gatekeeping rather than a one-off lapse. Second, and more pointedly, the dataset included 16 single-author reviews published in the Cochrane Database of Systematic Reviews itself — the flagship venue for an organization whose own Handbook explicitly recommends team-based, independent dual screening.
Why methodologists treat solo review selection as a risk factor
The concern predates this bibliometric paper by years and rests on separate empirical work quantifying what a second reviewer actually catches. A 2020 methodological systematic review in BMC Medical Research Methodology comparing single versus double screening found that a lone reviewer misses eligible studies that a second, independently-screening reviewer would have caught — on average a single screener misses a meaningful share of eligible reports that paired screening catches. A separate analysis specifically on study selection (published in the Journal of Clinical Epidemiology) found the average gain in eligible studies identified from adding a second reviewer was around 9%, ranging as high as 32% in some reviews — evidence that the effect is not a rounding error, and that its size varies a lot by review and search strategy. This is the empirical basis behind the standard PRISMA 2020 and Cochrane Handbook expectation that two reviewers screen titles/abstracts and full texts independently, then reconcile disagreements — a step the Institute of Medicine has separately argued is worth the added reviewer cost specifically because it reduces bias and error in the studies a review ultimately includes.
The tension for editors and institutions
None of this means every single-author review is unreliable, and the Shamsi et al. paper is careful not to claim that. Rapid reviews, scoping work, and narrowly-scoped updates to a living review sometimes have a legitimate case for a smaller team, and a solo author who documents deviations from dual-reviewer screening transparently is doing something different from one who is silent about it. What the data does establish is a gap between stated guidance and observed editorial practice: journals that publish, and endorse, PRISMA or Cochrane-aligned reporting standards are, per this dataset, still accepting single-author reviews at a non-trivial and apparently growing rate, without a consistent requirement that authors disclose or justify the departure from independent dual screening. The authors’ recommendations are aimed squarely at that gap — stricter editorial enforcement of collaborative authorship expectations for systematic reviews, research-assessment policies that don’t implicitly reward a single author racking up review “volume,” and clearer guidance from bodies such as COPE on how journals should handle disclosed single-author methodology.
What this means for research administrators and review teams
For research offices and journal-facing administrators, the practical takeaways are less about policing individual authors and more about where review processes can build in a checkpoint. Funders and institutions sponsoring evidence-synthesis work can ask, at proposal or protocol stage, whether screening and selection will be conducted independently by two or more reviewers, consistent with Cochrane Handbook and PRISMA expectations — the same question a PRISMA-P protocol registration effectively invites. Journals and editorial offices can treat “who screened, and how many people independently” as a standard methods-section disclosure to check at submission, the same way they already check for a completed PRISMA flow diagram. And review teams themselves — including solo doctoral candidates working on a systematic-review dissertation chapter — have a genuine, well-evidenced reason to bring in a second independent screener even informally, since the documented effect of a second reviewer on completeness is not small.
Related CASRAI resources
- PRISMA and Systematic Review Methodology — the full reporting-standard guide this trend sits against.
- How to Peer Review a Systematic Review or Meta-Analysis — what an independent reviewer should actually be checking for.
- Living Systematic Review Authorship — how rotating, multi-person contributor teams get credited on an evolving review.
- Cochrane Handbook for Systematic Reviews of Interventions
- PRISMA 2020
Sources
- Shamsi et al., “Single-Authored Systematic Reviews and Meta-Analyses: A Bibliometric Analysis of Trends and Alignment with Evidence-Based Medicine Guidelines,” Journal of Multidisciplinary Healthcare, 2025. DOI: 10.2147/JMDH.S545110.
- “Single screening versus conventional double screening for study selection in systematic reviews: a methodological systematic review,” BMC Medical Research Methodology, 2020.
- “The value of a second reviewer for study selection in systematic reviews,” Research Synthesis Methods / Journal of Clinical Epidemiology literature, PMID 31272125.
- Cochrane Handbook for Systematic Reviews of Interventions, Chapter 4 (training.cochrane.org/handbook).
- Page MJ et al., “The PRISMA 2020 statement,” BMJ 2021;372:n71.
