module Bayesab

Constants

VERSION

Public Class Methods

probability(control_success, control_fail, experiment_success, experiment_fail) click to toggle source

Calculates the likelyhood that control is an improvement on experiment.

Parameters:

control_success: Number of successes for the control group.
control_fail: Number of failures for the control group.
experiment_success: Number of successes for the experiment group.
experiment_fail: Number of failures for the experiment group.

# File lib/bayesab.rb, line 12
def self.probability(control_success, control_fail, experiment_success, experiment_fail)
  alpha_a = control_success + 1
  beta_a = control_fail + 1
  alpha_b = experiment_success + 1
  beta_b = experiment_fail + 1

  total = 0.0
  0.upto(alpha_b - 1) do |i|
    total += Math.exp(Math.lbeta(alpha_a + i, beta_b + beta_a)[0] - Math.log(beta_b + i) -
    Math.lbeta(1 + i, beta_b)[0] - Math.lbeta(alpha_a, beta_a)[0])
  end

  total
end