Question 2: The authors report 'We found a 46% reduction in the number of falls during the trial for the exercise group compared with the control group (incidence rate ratio 0.54, 95% confidence interval 0.32 to 0.90).' What is a 95% confidence interval? What does this tell us about the difference in incidence of falls?
We calculate a 95% confidence interval when we want a sample to tell us something about the larger population from which it is drawn. We estimate that the incident rate ratio for the whole population is within the interval. The interval is chosen so that 95% of intervals will contain their population value.
We estimate here that were we to offer the exercise programme to the whole population, the incidence rate of falls would be reduced by a factor between 0.32 and 0.90.
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Last updated: 23 October, 2006.