Cited by 1,483Meta-analysis and systematic reviewsPharmaceutical industry and healthcareAcademic Publishing and Open Access

The Mass Production of Redundant, Misleading, and Conflicted Systematic Reviews and Meta‐analyses

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IOANNIDIS, JOHN P.A.·2016·The Milbank Quarterly

Abstract

Policy Points : Currently, there is massive production of unnecessary, misleading, and conflicted systematic reviews and meta‐analyses. Instead of promoting evidence‐based medicine and health care, these instruments often serve mostly as easily produced publishable units or marketing tools. Suboptimal systematic reviews and meta‐analyses can be harmful given the major prestige and influence these types of studies have acquired. The publication of systematic reviews and meta‐analyses should be realigned to remove biases and vested interests and to integrate them better with the primary production of evidence. Context: Currently, most systematic reviews and meta‐analyses are done retrospectively with fragmented published information. This article aims to explore the growth of published systematic reviews and meta‐analyses and to estimate how often they are redundant, misleading, or serving conflicted interests. Methods: Data included information from PubMed surveys and from empirical evaluations of meta‐analyses. Findings: Publication of systematic reviews and meta‐analyses has increased rapidly. In the period January 1, 1986, to December 4, 2015, PubMed tags 266,782 items as “systematic reviews” and 58,611 as “meta‐analyses.” Annual publications between 1991 and 2014 increased 2,728% for systematic reviews and 2,635% for meta‐analyses versus only 153% for all PubMed‐indexed items. Currently, probably more systematic reviews of trials than new randomized trials are published annually. Most topics addressed by meta‐analyses of randomized trials have overlapping, redundant meta‐analyses; same‐topic meta‐analyses may exceed 20 sometimes. Some fields produce massive numbers of meta‐analyses; for example, 185 meta‐analyses of antidepressants for depression were published between 2007 and 2014. These meta‐analyses are often produced either by industry employees or by authors with industry ties and results are aligned with sponsor interests. China has rapidly become the most prolific producer of English‐language, PubMed‐indexed meta‐analyses. The most massive presence of Chinese meta‐analyses is on genetic associations (63% of global production in 2014), where almost all results are misleading since they combine fragmented information from mostly abandoned era of candidate genes. Furthermore, many contracting companies working on evidence synthesis receive industry contracts to produce meta‐analyses, many of which probably remain unpublished. Many other meta‐analyses have serious flaws. Of the remaining, most have weak or insufficient evidence to inform decision making. Few systematic reviews and meta‐analyses are both non‐misleading and useful. Conclusions: The production of systematic reviews and meta‐analyses has reached epidemic proportions. Possibly, the large majority of produced systematic reviews and meta‐analyses are unnecessary, misleading, and/or conflicted.

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  • Meta-analysis is indifferent to the quality of the original evidence.

    “is indifferent to the quality of the original evidence (14)”

    From Empirical audit and review and an assessment of evidentiary value in research on the psychological consequences of scarcity (2021) · cites this paper as [14]

    The Conclusion (page unavailable in our copy) says systematic reviews cannot be expected to correct deficiencies in primary evidence, supporting the concern behind the claim. But it also says they can reveal how unreliable published evidence is, so describing meta-analysis as simply indifferent to evidence quality overstates the paper's position. (LLM, conf=0.82)

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  • A priori registration of SR protocols could boost transparency, minimize outcome reporting bias, and reduce improper spending of research funds due overlaps between SRs.

    “Registered reviews offer better quality and conduct and reporting completeness compared to non-registered ones, and a priori registration of SR protocols could boost transparency, minimize outcome reporting bias, and reduce improper spending of research funds due overlaps between SRs [32–34].”

    From Reporting quality of abstracts of systematic reviews/meta-analyses: An appraisal of Arab Journal of Urology across 12 years: the PRISMA-Abstracts checklist (2023) · cites this paper as [34]

    The section “Flawed Meta-analyses and Correct but Noninformative Meta-analyses” (page unavailable) says that preregistering full protocols has been proposed to improve transparency. It does not say that registering systematic-review protocols reduces outcome-reporting bias or prevents spending on overlapping reviews; it also cautions that preregistration does not guarantee sound reporting. (LLM, conf=0.85)

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  • Registered reviews offer better quality and conduct and reporting completeness compared to non-registered ones.

    “Registered reviews offer better quality and conduct and reporting completeness compared to non-registered ones, and a priori registration of SR protocols could boost transparency, minimize outcome reporting bias, and reduce improper spending of research funds due overlaps between SRs [32–34].”

    From Reporting quality of abstracts of systematic reviews/meta-analyses: An appraisal of Arab Journal of Urology across 12 years: the PRISMA-Abstracts checklist (2023) · cites this paper as [34]

    In “Flawed Meta-analyses and Correct but Noninformative Meta-analyses” (page unavailable), the paper says preregistration has been proposed to improve transparency and perhaps quality. It does not establish that registered reviews have better conduct or more complete reporting than non-registered reviews; it cautions that registration does not guarantee sound conduct or reporting. (LLM, conf=0.85)

    Experimental — accuracy not yet measured
  • Many systematic reviews continue to be poorly conducted and reported.

    “However, many SRs continue to be poorly conducted and reported [10, 11]”

    From How to properly use the PRISMA Statement (2021) · cites this paper as [11]

  • The number of published systematic reviews has increased exponentially in recent years.

    “The number of published systematic reviews has increased exponentially in recent years [18, 19].”

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Research works printed but not linked: 5

  1. [11]11. Olkin I. Meta-analysis: current issues in research synthesis. Stat Med. 1996;15(12):1253-1257; discussion 1259-1262.
  2. [14]14. Iqbal SA, Wallach JD, Khoury MJ, Schully SD, Ioannidis JP. Re- producible research practices and transparency across the biomed- ical literature. PLoS Biol. 2016;14(1):e1002333.
  3. [40]40. Ebrahim S, Montoya L, el Din MK, et al. Secondary publications from randomized controlled trials: a meta-epidemiological study. J Clin Epidemiol. In press.
  4. [45]45. Horrobin DF. Beyond conflict of interest. Non-financial con- flicts of interest are more serious than financial conflicts. BMJ. 1999;318(7181):466.
  5. [89]89. Moher D, Tetzlaff J, Tricco AC, Sampson M, Altman DG. Epi- demiology and reporting characteristics of systematic reviews. PLoS Med. 2007;4(3):e78.

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Authors
IOANNIDIS, J. P. A.
Affiliations
Stanford Medicine (US)
Corresponding author
IOANNIDIS, JOHN P.A.
Venue
The Milbank Quarterly
Publisher
Wiley
Published
2016-09
Volume
94
Issue
3
Pages
485-514
ISSN
  • 0887-378X (ISSN-L)
  • 1468-0009
OpenAlex
W2520714999
Cited by
1,483
References
116
Citations by year
2026: 122 · 2025: 150 · 2024: 125 · 2023: 165 · 2022: 184 · 2021: 191 · 2020: 166 · 2019: 141 · 2018: 142 · 2017: 81 · 2016: 15 · 2015: 1
FWCI
43.35
Type
journal article
Language
en
Open access
Locations
  • Milbank Quarterly (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • Laura and John Arnold Foundation
  • Stanford Bio-X
Topics
  • Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
  • Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmaceutical industry and healthcare
  • Social Sciences › Decision Sciences › Information Systems and Management › Academic Publishing and Open Access
Keywords
systematic reviews, meta-analysis, publication growth, redundancy, conflicts of interest, industry funding, research bias, evidence synthesis, candidate genes, evidence-based medicine, research integrity, contracting companies
MeSH terms
Antidepressive Agents, Genetics, Deception, Quality Control, Review Literature as Topic, Meta-Analysis as Topic, Bias, Randomized Controlled Trials as Topic, Evidence-Based Medicine

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