Calculate lower bound of Wilson score confidence interval for a Bernoulli parameter

score_binomial_rating.py

import math
import scipy.stats as stats

"""
Algorithms desgin:
http://www.evanmiller.org/how-not-to-sort-by-average-rating.html
What: Calculate lower bound  of Wilson score confidence interval for a Bernoulli parameter
Why: Sort data by binomial votes score
"""
def ci_lower_bound(pos, n, confidence):
    if n == 0:
        return 0
    z = stats.norm.ppf(1-(1-confidence)/2)
    phat = 1.0*pos/n
    return (phat + z*z/(2*n) - z * math.sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n)


if __name__ == "__main__":
	from sys import argv
	#pos, n , confidence = (sys.argv[1], sys.argv[2], sys.argv[3])
	print ci_lower_bound(float(argv[1]), float(argv[2]), float(argv[3]))