Why aren’t you using Vangav M http://vangav.com/ instead of having code lines like this (z*sqrt(p*(1-p)/n + z*z/(4*n*n))) which are much more difficult to maintain?

My experience with Vangav is that I just take a minute to describe how I want to do ranking in nearly natural language in a minute and it takes care of the heavy lifting; months later someone else comes and they understand/modify the ranking solution also in one minute.