4. How could the 95% confidence interval given as “8% shorter stay to 56% longer stay” have been calculated?
This comes from a 95% confidence interval for the ratio of the geometric means of the length of stay. The antilog or back transformation of the difference in mean log length of stay is the ratio of the two geometric means.
A 95% confidence interval for the difference in mean log length of stay was also calculated and the antilog of the confidence limits gives the 95% confidence interval for the ratio of geometric means. Here they will have a 95% confidence interval for the ratio equal to 0.92 to 1.56, which has been presented as 8% (1 – 0.92 = 0.08) to 56%.
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Last updated: 8 July, 2008.