To the extent that users can influence the direction of the software, I would vote to keep the CI about a proportion as they are (or provide the user an option to choose between "exact" method and the simple test-based, or Wald approximation). OpenEpi provides 6 different CI about a proportion, one of which is symmetric, while the others are various approximations to the exact (asymmetric) CI.
In most situations, the differences will not be important. However, when working with small numbers as in many outbreaks, the "exact" CI may be preferred.
Certainly, a short document on statistical methods employed will be useful. I'm happy to help write that.
Jamie
On 2011-02-16, Ajay wrote:
Query - why are the two limbs of the confidence interval [about a proportion] different?