Suggested answer to exercise: Estimation, standard error and confidence intervals, 5

Question 5: Explain why this 95% confidence interval is narrower than that reported in the UK study. Do you think that there is a real difference in preterm birth rates between the two populations being studied?

Suggested answer

The Danish study included many more subjects than the UK study and so the estimate of preterm birth incidence is much more precise. Hence the 95% confidence interval is narrower. The percentage preterm in the UK study is 3 percentage points higher than in the Danish study and the two 95% confidence intervals do not overlap. Hence there some evidence for a real difference.

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Last updated: 27 July, 2009.

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