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Table 2 Demonstration of Simpson's paradox in the pooling of data from three observational studies, showing the value of meta-analysis

From: Bench-to-bedside review: Avoiding pitfalls in critical care meta-analysis – funnel plots, risk estimates, types of heterogeneity, baseline risk and the ecologic fallacy

 

Mortality

  
 

Treatment

Placebo

Risk ratioa

Significance

Study 1

97/492 = 19.7%

202/802 = 24.8%

0.794

0.03

Study 2

590/795 = 74.2%

410/510 = 80.4%

0.924

0.01

Study 3

300/610 = 49.2%

286/490 = 58.4%

0.843

0.002

Pooled data

987/1,897 = 52.0%

898/1,812 = 49.6%

1.050

0.13

  1. Meta-analysis of the above data (using [40]), fixed-effects model: Q statistic = 3.398, P = 0.18; combined risk ratio = 0.898, P = 0.0001.
  2. aTreatment/placebo.
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Critical Care

ISSN: 1364-8535