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Of mites and men: reference bias in narrative review articles: a systematic review
Lasse M Schmidt1, Peter C Gotzsche
1Nordic Cochrane Centre, Copenhagen, Denmark.
Background:
Citations in scientific articles may tend to favor the views presented. We studied whether there is such reference bias in narrative review articles that discuss interventions against house dust mites for people with asthma.
Design:
Systematic review of reviews identified in a Medline search that expressed an opinion about the clinical effects of physical or chemical intervention methods.
Main Outcome Measure:
Positive bias was judged to have occurred if the reference list contained a higher proportion of trial references with significant results than among all trials available to the authors (published 2 years or more prior to the review).
Results:
Seventy reviews were included, of which 63 (90%) recommended physical interventions. Forty-six reviews had trial references, 4 of these only to chemical interventions. In the remaining 42 reviews, reference bias was detected (P=2 x 10-8). The most quoted trial had only 7 patients per group, its claimed significant result was probably erroneous, and it did not report a clinical outcome. Intervention recommendations were often based on nonrandomized evidence, and the most quoted nonrandomized controlled study had included only 10 patients per group but claimed very positive results.
Conclusion:
The narrative review articles were severely biased, and their positive intervention recommendations are at variance with the systematic Cochrane Review on this topic and a recent very large trial of physical intervention, both of which failed to find an effect.
Insights
Scientific reviews on house dust mite interventions for asthma show significant reference bias. Many recommendations favor interventions despite limited or flawed evidence, contradicting larger, more robust studies.
Area of Science:
- Allergy and Immunology
- Respiratory Medicine
- Evidence-Based Medicine
Background:
- Scientific literature may exhibit citation bias, favoring presented viewpoints.
- This study investigates reference bias in narrative reviews concerning house dust mite interventions for asthma patients.
Purpose of the Study:
- To determine if reference bias exists in narrative review articles on interventions for asthma triggered by house dust mites.
- To assess the influence of bias on intervention recommendations.
Main Methods:
- A systematic review of narrative reviews identified via Medline search.
- Reviews focused on clinical effects of physical or chemical interventions for asthma.
- Positive bias was defined as a higher proportion of significant trial results in the reference list compared to available trials (published ≥2 years prior).
Main Results:
- Seventy reviews were analyzed; 90% recommended physical interventions.
- Reference bias was detected in 42 reviews (P=2 x 10-8).
- Recommendations were often based on non-randomized or small, potentially erroneous trials, with some lacking clinical outcome data.
Conclusions:
- Narrative review articles on house dust mite interventions for asthma exhibit severe bias.
- Positive intervention recommendations contradict findings from the Cochrane Review and a large recent trial, which found no significant effect.
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