Question 3: How would the confidence interval change if 90% limits were used?
If 90% limits were used the confidence interval would be narrower and fewer (90% rather than 95%) of confidence intervals from possible samples would contain the population incidence. Thus the estimated range of possible values would be narrower but there would be more chance of being wrong. (The 90% confidence limits would be 6.4 to 8.6%).
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