**StATS: **Asymmetric confidence intervals (created 1999-09-03)

*Dear Professor Mean, I found a journal article with a confidence interval
that was asymmetric. For example, the authors reported a mortality difference
of 5% and a 95% confidence interval of -1.2% to 12%. I can't understand how the
CI can be unequally distributed if it uses the form ESTIMATE +/- 1.96*STANDARD
*

**Not every confidence interval uses a plus or minus type formula**.
The ones that don't are usually asymmetric. In particular, **most
confidence intervals involving ratios are asymemmetric** (though some
of them are symmetric on a log scale). Also **confidence intervals that
take the small sample sizes into account are often asymmetric**. It's
good that you remember your confidence interval formula from your Statistics
class, but your instructor probably didn't have time to show you every
possible confidence interval formula.

This page was written by Steve Simon while working at Children's Mercy Hospital. Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Category: Confidence intervals.