Python implementation of the Wilson Score Interval?

python algorithm statistics ranking
Jeff Bauer picture Jeff Bauer · Apr 5, 2012 · Viewed 10.7k times · Source

After reading How Not to Sort by Average Rating, I was curious if anyone has a Python implementation of a Lower bound of Wilson score confidence interval for a Bernoulli parameter?

Answer

Steef picture Steef · Apr 5, 2012

Reddit uses the Wilson score interval for comment ranking, an explanation and python implementation can be found here 

#Rewritten code from /r2/r2/lib/db/_sorts.pyx

from math import sqrt

def confidence(ups, downs):
    n = ups + downs

    if n == 0:
        return 0

    z = 1.0 #1.44 = 85%, 1.96 = 95%
    phat = float(ups) / n
    return ((phat + z*z/(2*n) - z * sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n))

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