Bayesian experiment comparison

bayesian.rb

require 'distribution'

# set these values
control_success = 338
control_fail = 56
experiment_success = 341
experiment_fail = 53

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

puts total