wilson score confidence interval - what percentage of people took some sort of action

gistfile1.rb

#pos is the number of positive ratings
#n is the total number of ratings
def score_ratings(pos, n)
    #modified shamelessly from http://evanmiller.org/how-not-to-sort-by-average-rating.html
    return 0 if n == 0
    # require 'statistics2'
    # z = Statistics2.pnormaldist(1-(1-confidence)/2)
    # the z score refers to a confidence: pick 0.95 to have a 95% chance that your lower bound is correct, 0.975 to have a 97.5% chance, etc. 
    # (Uses #1.96 for a confidence level of 0.95.)
    z = 1.96
    phat = 1.0*pos/n
    (phat + z*z/(2*n) - z * Math.sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n)
end