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Systematic reviews and meta-analyses on treatment of asthma: critical evaluation

BMJ 2000; 320 doi: (Published 26 February 2000) Cite this as: BMJ 2000;320:537

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  1. Alejandro R Jadad, professor (jadada{at},
  2. Michael Moher, Royal College of General Practitioners research training fellowb,
  3. George P Browman, professora,
  4. Lynda Booker, research assistanta,
  5. Christopher Sigouin, doctoral studenta,
  6. Mario Fuentes, research assistantc,
  7. Robert Stevens, research assistantc
  1. a Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada L8N 3Z5
  2. b Institute of Health Sciences, University of Oxford, Headington, Oxford OX3 7LF
  3. c Foresight Consultants, Dundas, Ontario, Canada L9H 2R5
  1. Correspondence to: A R Jadad
  • Accepted 13 December 1999


Objective: To evaluate the clinical, methodological, and reporting aspects of systematic reviews and meta-analyses on the treatment of asthma and to compare those published by the Cochrane Collaboration with those published in paper based journals.

Design: Analysis of studies identified from Medline, CINAHL, HealthSTAR, EMBASE, Cochrane Library, personal collections, and reference lists.

Studies: Articles describing a systematic review or a meta-analysis of the treatment of asthma that were published as a full report, in any language or format, in a peer reviewed journal or the Cochrane Library.

Main outcome measures: General characteristics of studies reviewed and methodological characteristics (sources of articles; language restrictions; format, design, and publication status of studies included; type of data synthesis; and methodological quality).

Results: 50 systematic reviews and meta-analyses were included. More than half were published in the past two years. Twelve reviews were published in the Cochrane Library and 38 were published in 22 peer reviewed journals. Forced expiratory volume in one second was the most frequently used outcome, but few reviews evaluated the effect of treatment on costs or patient preferences. Forty reviews were judged to have serious or extensive flaws. All six reviews associated with industry were in this group. Seven of the 10 most rigorous reviews were published in the Cochrane Library.

Conclusions: Most reviews published in peer reviewed journals or funded by industry have serious methodological flaws that limit their value to guide decisions. Cochrane reviews are more rigorous and better reported than those published in peer reviewed journals.


  • Funding Foresight Consultants was commissioned by AstraZeneca Research and Development Lund, Sweden, and AstraZeneca US to perform an independent review of this topic through an unrestricted contract. Representatives from AstraZeneca did not participate in the study selection or appraisal or in the analysis of the data. ARJ was supported in part by a National Health Research Scholar Award from Health Canada, Ottawa, Ontario.

  • Competing interests ARJ is codirector of the Canadian Cochrane Network and Centre.

  • website extra: Details of the search strategy and all included studies are available on the BMJ's website

  • Accepted 13 December 1999
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