Lower bound of Wilson score confidence interval for a Bernoulli parameter

lower_bound.go

// Golang implementation of Evan Miller's algorithm for ranking stuff based on upvotes: 
// http://www.evanmiller.org/how-not-to-sort-by-average-rating.html

// playground link: https://play.golang.org/p/dV6yk6pBY5y

func lowerBound(upvotes, n int, confidence float64) (float64, error) {
	if n == 0 {
		return 0, errors.New("n can't be 0")
	}
    
	floatN := float64(n)
    
	phat := float64(1.0 * upvotes / n)
    
	z := math.Erfinv(1 - (1-confidence)/2)

	result := (phat + z*z/(2*floatN) - z*math.Sqrt((phat*(1-phat)+z*z/(4*floatN))/floatN)) / (1 + z*z/floatN)
    
	return result, nil
}