class DanbooruMath
  def self.ci_lower_bound(pos, n, confidence = 0.95)
    if n == 0
      return 0
    end

    z = Statistics2.pnormaldist(1 - (1 - confidence) / 2)
    phat = 1.0 * pos / n
    100 * (phat + z * z / (2 * n) - z * Math.sqrt((phat * (1 - phat) + z * z / (4 * n)) / n)) / (1 + z * z / n)
  end
end