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Table 2 Results of meta-analyses of trials of high intensity nursing to reduce smoking using standard§ and 'treat-as-one-trial' methods, with relative risk as effect measure

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

Setting (no. of trials) Number quitting/total Pooled risk ratio (95% CI) NNT (95% CI)
  Intervention Control   
Hospital (7) 435/1367 318/1295   
   Meta-analysis    1.30 (1.16 to 1.47) 13.6 (8.7 to 25.5)¶¶
   Treat-as-one-trial    1.30 (1.15 to 1.47) 13.8 (9.4 to 25.9)
Primary Care (3) * 111/2453 41/1006   
   Meta-analysis    1.01 (0.71 to 1.42) 2454 (58.4 to H84.6)¶¶
   Treat-as-one-trial    1.11 (0.78 to 1.58) 222.5 (52.0 to H97.7)
Primary Care (2) ** 87/2246 25/958   
   Meta-analysis    1.54 (0.97 to 2.44) 71.0 (26.6 to H1277)¶¶
   Treat-as-one-trial    1.48 (0.96 to 2.30) 79.1(39.2 to H4369)
  1. § Mantel-Haenszel method (fixed effect) * as defined by Moore et al ** excluding reference [12] NNT for harm [13]¶¶NNT calculated using the event rate among controls and the relative risk reduction [4]