hummingbird-me/hummingbird

class WilsonScore
  def self.lower_bound(pos, n)
    return 0 if n == 0

    # z=1.96 corresponds to confidence=0.95
    # z=2.17 corresponds to confidence=0.97
    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
end