TableĀ 1

Application of flow diagram approach to Scenario 1

1. Research questionIs posturing advisable in patients undergoing vitrectomy surgery?
2. Null hypothesisThere is no difference in risk of failure between patients undergoing vitrectomy surgery in Group A (posturing) and Group B (no posturing).
3. ResultOdds in Group A=1/199
Odds in Group B=2/198
95% CI=0.18 to 22.3
4. InterpretationThe best estimate of the OR is 2, that is, failure is twice as common in the non-posturing group as it is the posturing group. There is however a lot of uncertainty with this estimate. The trial data means that it is plausible that the odds are the same in the two groups; however it is still possible that the odds are actually more than 20 times in the non-posturing group or as little as a fifth as high. If we were to simply consider the p value none of this uncertainty would be apparent and we would be far more tempted to simply say that there is no evidence of a difference in failure rates.