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Table 1 Results of meta-analyses of trials of nicotine gum to reduce smoking using standard and 'treat-as-one-trial' methods, with risk difference as effect measure

From: Meta-analysis, Simpson's paradox, and the number needed to treat

  Pooled risk difference (95% CI) P NNT
(a) Two selected trials (see text)    
   Standard meta-analysis (Mantel-Haenszel method) 0.060 (0.025 to 0.095) 0.001 16.7
   Treat-as-one-trial 0.033 (0.001 to 0.064) 0.04 30.7
(b) All 51 trials    
   Standard meta-analysis (Mantel-Haenszel method) 0.061 (0.050 to 0.071) <0.001 16.4
   Treat-as-one-trial 0.081 (0.070 to 0.092) <0.001 12.3