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Cited by 919Meta-analysis and systematic reviewsAdvanced Causal Inference TechniquesStatistical Methods in Clinical Trials

The DOI matches its Crossref record; 49 of the 50 references it cites were found in a registry or an index.

Comparison of Evidence of Treatment Effects in Randomized and Nonrandomized Studies

Ioannidis, John P. A.·2001·JAMA
DOI 10.1001/jama.286.7.821
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Abstract

CONTEXT: There is substantial debate about whether the results of nonrandomized studies are consistent with the results of randomized controlled trials on the same topic. OBJECTIVES: To compare results of randomized and nonrandomized studies that evaluated medical interventions and to examine characteristics that may explain discrepancies between randomized and nonrandomized studies. DATA SOURCES: MEDLINE (1966-March 2000), the Cochrane Library (Issue 3, 2000), and major journals were searched. STUDY SELECTION: Forty-five diverse topics were identified for which both randomized trials (n = 240) and nonrandomized studies (n = 168) had been performed and had been considered in meta-analyses of binary outcomes. DATA EXTRACTION: Data on events per patient in each study arm and design and characteristics of each study considered in each meta-analysis were extracted and synthesized separately for randomized and nonrandomized studies. DATA SYNTHESIS: Very good correlation was observed between the summary odds ratios of randomized and nonrandomized studies (r = 0.75; P<.001); however, nonrandomized studies tended to show larger treatment effects (28 vs 11; P =.009). Between-study heterogeneity was frequent among randomized trials alone (23%) and very frequent among nonrandomized studies alone (41%). The summary results of the 2 types of designs differed beyond chance in 7 cases (16%). Discrepancies beyond chance were less common when only prospective studies were considered (8%). Occasional differences in sample size and timing of publication were also noted between discrepant randomized and nonrandomized studies. In 28 cases (62%), the natural logarithm of the odds ratio differed by at least 50%, and in 15 cases (33%), the odds ratio varied at least 2-fold between nonrandomized studies and randomized trials. CONCLUSIONS: Despite good correlation between randomized trials and nonrandomized studies-in particular, prospective studies-discrepancies beyond chance do occur and differences in estimated magnitude of treatment effect are very common.

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Metadata

Authors
Ioannidis, J. P. A.
Affiliations
Tufts Medical Center (US)
Corresponding author
Ioannidis, John P. A.
ORCID
Ioannidis, John P. A.
Venue
JAMA
Publisher
American Medical Association (AMA)
Published
2001-08-15
Volume
286
Issue
7
Pages
821
ISSN
  • 0002-9955 (ISSN-L)
  • 0098-7484
DOI
10.1001/jama.286.7.821
OpenAlex
W2084917404
Cited by
919
References
50
Citations by year
2026: 11 · 2025: 18 · 2024: 39 · 2023: 24 · 2022: 46 · 2021: 59 · 2020: 53 · 2019: 39 · 2018: 31 · 2017: 41 · 2016: 39 · 2015: 40 · 2014: 42 · 2013: 45 · 2012: 39
FWCI
58.25
Type
journal article
Language
en
Open access
closed
Locations
  • JAMA (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
  • Physical Sciences › Mathematics › Statistics and Probability › Advanced Causal Inference Techniques
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
Keywords
randomized controlled trials, non-randomized studies, observational studies, treatment effect estimates, odds ratio, study heterogeneity, prospective study, medical interventions, publication timing
MeSH terms
Clinical Trials as Topic, Data Interpretation, Statistical, Humans, Meta-Analysis as Topic, Randomized Controlled Trials as Topic, Evidence-Based Medicine

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