RLO: Confidence Intervals

 

The width of the confidence interval

In our heart attack example, the true effect of the intervention lies within a wide range and the trial is not very informative.  In the table on the right, look at what happens when our trial is repeated in a larger number of patients. The relative risk reduction has stayed the same, but try manipulating the figures as before and see what happens.

You can see that not only has the trial now reached statistical significance, but the confidence intervals become narrower with a bigger trial.  The narrower the confidence interval, the more sure you can be of the true size of the effect of the intervention.

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