Course Notes - Department of Mathematics and Statistics

INCONCLUSIVE CONFIDENCE INTERVALSNote that in practice the researcher decides what is clinically/ecologicallysignificant. If the confidence interval contains both 0 and the clinicallyimportant difference then the result is inconclusive. The p-valuerelates to whether or not the confidence interval includes 0 - if zero isincluded then the p-value > 0.05 (and vice versa).7.7 PowerA FURTHER EXAMPLEA clinical trial is set up to compare two drugs (statin, A, and acontrol, B) for lowering cholesterol. The mean cholesterol reductionsin the two groups are compared. The probability that such a study willcorrectly detect a clinically important difference between the effectsof the drugs is called the POWER of the study. Power depends on:• the size of the difference,• the variability of estimates (σ),• the sample size (n), and• the level of significance (α).As the sample size increases, the confidence intervals become samllerand it is possible to detect the difference.133