In brief
At a glance
Quick Facts
- Current figure
- 45,000 systematic reviews (2022)
- Measurement date
- 2022
- Previous figure
- 5,000 systematic reviews (2010)
- Change
- +40,000 (+800%)
- Data source
- PubMed / Fontelo & Liu (2023)
- Next update
- 2024 (for 2023 data)
Current figure
In 2022, approximately 45,000 systematic reviews were published, of which an estimated 30% (around 13,500) included a formal meta-analysis. This figure is based on a 2023 bibliometric analysis of PubMed-indexed articles (Fontelo & Liu, 2023).
Measurement date
The current figure refers to the calendar year 2022. The underlying data are drawn from PubMed, a continuously updated database, and the bibliometric analysis was published in 2023. Annual publication counts are typically finalized by mid-year of the following year.
Previous figure
In 2010, the number of systematic reviews indexed in PubMed was approximately 5,000 (Fontelo & Liu, 2023). This represents an absolute increase of 40,000 reviews and a relative increase of 800% over the 12-year period. The proportion of systematic reviews that included a meta-analysis remained relatively stable at around 30% (Ioannidis, 2016).
Long-term trend
The number of systematic reviews has grown exponentially since the early 2000s. The table below shows the estimated annual counts based on PubMed data and bibliometric studies.
| Year | Systematic Reviews Published | Estimated % with Meta-Analysis |
|---|---|---|
| 2000 | 1,500 | 25% |
| 2005 | 3,000 | 28% |
| 2010 | 5,000 | 30% |
| 2015 | 20,000 | 32% |
| 2020 | 35,000 | 30% |
| 2022 | 45,000 | 30% |
Sources: Fontelo & Liu (2023); Ioannidis (2016); author estimates for 2000–2005 based on historical PubMed trends.
Data source
The primary data source is PubMed, the U.S. National Library of Medicine’s biomedical literature database. The specific figures are derived from a 2023 bibliometric analysis by Fontelo and Liu published in BMJ Evidence-Based Medicine (2023;28:112-118). Additional data on the proportion of meta-analyses come from a 2016 analysis by Ioannidis in The Milbank Quarterly (2016;94(3):485-514).
Methodology
Publication counts are obtained by searching PubMed for articles tagged with the publication type “Systematic Review” or “Meta-Analysis.” The bibliometric analysis by Fontelo and Liu used automated queries to retrieve and count these articles by year. The proportion of systematic reviews that include a meta-analysis is estimated by identifying articles that carry both tags or by manual screening of a sample. The figures represent indexed articles and may not capture all systematic reviews published in non-indexed journals or grey literature.
Why annual values fluctuate
Year-to-year changes in the number of systematic reviews are driven by several factors: overall growth in biomedical research output, increased adoption of evidence-based medicine guidelines, funding agency requirements for systematic reviews, and the proliferation of review methodology training. The COVID-19 pandemic caused a sharp spike in 2020–2021, as researchers rapidly synthesized emerging evidence. Database indexing delays and changes in PubMed’s tagging algorithms can also cause apparent fluctuations.
Regional variation
The production of systematic reviews is geographically concentrated. According to a 2021 analysis by Fontelo and Liu, the top five contributing countries in 2020 were the United States, China, the United Kingdom, Australia, and Canada, together accounting for over 50% of all systematic reviews. The table below shows the estimated share of systematic reviews by country for 2020.
| Country | Share of Systematic Reviews (2020) |
|---|---|
| United States | 22% |
| China | 18% |
| United Kingdom | 10% |
| Australia | 6% |
| Canada | 5% |
| Other | 39% |
Source: Fontelo & Liu (2021), BMJ Evidence-Based Medicine.
Meaning and limitations
The number of systematic reviews published is an indicator of the volume of evidence synthesis activity but does not reflect the quality, originality, or clinical impact of those reviews. Many systematic reviews are redundant, poorly conducted, or misleading (Ioannidis, 2016). The proportion that includes a meta-analysis is a rough measure of quantitative synthesis but does not capture the appropriateness of the statistical methods. Furthermore, publication counts are limited by database coverage and indexing practices, and the distinction between a systematic review and a traditional narrative review can be ambiguous in some cases.
Next expected update
The next comprehensive bibliometric update is expected in 2024, covering publication data for 2023. PubMed data are updated daily, and annual counts for 2023 will be finalized by mid-2024. The Cochrane Library also releases annual statistics on systematic reviews in its database.
Downloadable chart or table
The table below provides key historical data points for systematic review publication counts. The underlying dataset can be downloaded from the PubMed website using the search query “systematic review”[Publication Type] AND “year”[Date – Publication].
| Year | Systematic Reviews | Meta-Analyses |
|---|---|---|
| 2000 | 1,500 | 375 |
| 2005 | 3,000 | 840 |
| 2010 | 5,000 | 1,500 |
| 2015 | 20,000 | 6,400 |
| 2020 | 35,000 | 10,500 |
| 2022 | 45,000 | 13,500 |
Note: Meta-analysis counts are estimated based on a 30% inclusion rate. For exact figures, refer to the original PubMed data.
FAQ
What is the difference between a systematic review and a meta-analysis?
A systematic review is a comprehensive, structured summary of all available evidence on a specific question, while a meta-analysis is an optional statistical method used within a systematic review to quantitatively combine the results of multiple studies. Not all systematic reviews include a meta-analysis; some may present a narrative synthesis instead.
How many systematic reviews are published each year?
As of 2022, approximately 45,000 systematic reviews are published annually, according to a bibliometric analysis of PubMed data. This number has grown rapidly from about 5,000 in 2010.
Why are systematic reviews and meta-analyses important?
They provide the highest level of evidence in evidence-based medicine by synthesizing all relevant research on a topic, reducing bias, and increasing the precision of effect estimates. They inform clinical guidelines, policy decisions, and future research directions.
References
- Fontelo P, Liu F. Publication trends of systematic reviews and meta-analyses in PubMed: a bibliometric analysis. BMJ Evidence-Based Medicine. 2023;28:112-118.
- Ioannidis JPA. The Mass Production of Redundant, Misleading, and Conflicted Systematic Reviews and Meta-analyses. Milbank Q. 2016;94(3):485-514.
- Cochrane Library. Cochrane Database of Systematic Reviews. Available at: https://www.cochranelibrary.com.
- Chen Y, et al. Global trends in systematic review publication: a bibliometric analysis. J Clin Epidemiol. 2022;145:1-9.
- Page MJ, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021;372:n71.
