How do two meta-analyses of similar data reach opposite conclusions?

BMJ 1999;318:873 ( 27 March )

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How do two meta-analyses of similar data reach opposite conclusions?

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EDITOR $---$ In their meta-analysis Fahey et al concluded that treatment with antibiotics made no significant difference to theresolution of acute cough,¹ although they found a trend favouringantibiotics. The Cochrane meta-analysis on treatment of acutebronchitis concluded that antibiotics have a modest beneficialeffect.² Eight of the nine studies extracted were the samein both meta-analyses, and 90% of the 750 patients were used inboth.

How can two meta-analyses based on the same studies come to opposite conclusions? In Fahey et al's study the outcome measureswere resolution of cough and clinical improvement on re-examination.In the Cochrane meta-analysis, four outcomes showed significantdifferences between antibiotic treatment and placebo. The patientswere less likely to report feeling unwell at a follow up visit(two studies), to show no improvement on assessment by a doctor(four studies), and to have abnormal lung findings (two studies)and had a more . . . [Full text of this article]

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Quantitative systematic review of randomised controlled trials comparing antibiotic with placebo for acute cough in adults: Tom Fahey, Nigel Stocks, and Toby Thomas
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