Statistics notes. Treatment allocation in controlled trials: why randomise?
Open accessAbstract
Since 1991 the BMJ has had a policy of not publishing trials that have not been properly randomised, except in rare cases where this can be justified.1 Why? The simplest approach to evaluating a new treatment is to compare a single group of patients given the new treatment with a group previously treated with an alternative treatment. Usually such studies compare two consecutive series of patients in the same hospital(s). This approach is seriously flawed. Problems will arise from the mixture of retrospective and prospective studies, and we can never satisfactorily eliminate possible biases due to other factors (apart from treatment) that may have changed over time. Sacks et al compared trials of the same treatments in which randomised or historical controls were used and found a consistent tendency for historically controlled trials to yield more optimistic results than randomised trials.2 The use of historical controls can be justified only in tightly controlled situations of relatively rare conditions, such …
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Inferential statistics based on nonrandomised group allocation are not valid.
“Inferential statistics based on nonrandomised group allocation are not valid [65,66].”
From Reporting animal research: Explanation and elaboration for the ARRIVE guidelines 2.0 (2020) · cites this paper as [66]
Altman and Bland explain that random allocation lets treatment-group differences be assessed using statistical theory about random samples (p. 1209). They also describe bias risks in nonrandomised comparisons, but do not say that all inferential statistics based on nonrandomised allocation are invalid; they acknowledge situations where randomisation is not possible. (LLM, conf=0.85)
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Cites
Improving the Quality of Reporting of Randomized Controlled Trials: The CONSORT Statement
Begg, C. (1996) · JAMA · doi:10.1001/jama.1996.03540080059030 · Cited by 3,127 · see citing works
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Research works printed but not linked: 5
- Altman DG. Randomisation. BMJ 1991;302:1481-2.
- Sacks H, Chalmers TC, Smith H. Randomized versus historical controls for clinical trials. Am J Med 1982;72:233-40.
- MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council vitamin study. Lancet 1991;338:131-7.
- Medical Research Council. Streptomycin treatment of pulmonary tuber- culosis. BMJ 1948;2:769-82.
- Black N. Why we need observational studies to evaluate the effectiveness of health care. BMJ 1996;312:1215-8.
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- Authors
- Altman, D. G., & Bland, J. M.
- Affiliations
- University of Oxford (GB)
- St George's, University of London (GB)
- ORCID
- Altman, D. G
- Venue
- BMJ
- Publisher
- BMJ
- Published
- 1999-05-01
- Volume
- 318
- Issue
- 7192
- Pages
- 1209-1209
- ISSN
- 0007-1447 (ISSN-L)
- 0959-8138
- 1468-5833
- PMC
- PMC1115595
- OpenAlex
- W2017329532
- Cited by
- 362
- References
- 1
- Citations by year
- 2026: 14 · 2025: 11 · 2024: 15 · 2023: 14 · 2022: 17 · 2021: 19 · 2020: 19 · 2019: 17 · 2018: 13 · 2017: 12 · 2016: 19 · 2015: 12 · 2014: 13 · 2013: 16 · 2012: 17
- FWCI
- 11.10
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- BMJ (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- HighWire Press Open Archive (submittedVersion)
- Topics
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Physical Sciences › Mathematics › Statistics and Probability › Advanced Causal Inference Techniques
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Keywords
- randomization, treatment allocation, historical controls, bias, publication policy, trial design, confounding
- MeSH terms
- Randomized Controlled Trials as Topic, Patient Selection
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