BMJ 1995;311:753-754 (16 September)

Letters

Misleading meta-analysis

EDITOR,--In their response1 to our editorial on misleading meta-analysis2 A Perry and R Persaud state that we ignored the degree of heterogeneity among different studies. We examined the case of intravenous magnesium in acute myocardial infarction, a treatment recently shown to be of no benefit in a trial.3 We argued that the asymmetrical funnel plot (a plot of the estimates of effect sizes against the sample size) should have alerted meta-analysts to the possible presence of bias. The erroneous conclusion that magnesium treatment represents an "effective, safe, simple and inexpensive" intervention could thus have been prevented.4 5

Perry and Persaud argue that, rather than funnel plots being used, a statistical test of homogeneity should be performed to help decide whether the results of meta-analysis of small trials should be endorsed or distrusted. They seem, however, to be unaware of the extensive literature about the limitations of this test. The test for . . . [Full text of this article]


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Relevant Article

Registers for clinical trials already exist
J A Muir Gray
BMJ 1995 310: 1604. [Extract] [Full Text]

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