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Binomial Test

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• Overview:

  Script for calculating a p-value of binomial test, which is also used in McNemar's test.
  This script calculates the exact 2-side p-value.
  

• Usage:

   python binomial-test.py num1 num2
  
   where                       baseline true    baseline false
             proposed true     *                num1
             proposed false    num2             *
  

• Example:

   Command:
     python binomial-test.py 25250 24750
  
   Output:
     num1 = 25250, num2 = 24750, p = 0.0256407074758939
  

• Script: (binomial-test.py)

  #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  
  from __future__ import print_function
  import sys
  
  if __name__=='__main__': 
      argvs = sys.argv
      if len(argvs) < 3 or not argvs[1].isdigit() or not argvs[2].isdigit():
          print("Usage: {0} num1 num2".format(argvs[0]))
          sys.exit()   
  
      if int(argvs[1]) == int(argvs[2]):
          print("num1 = {0}, num2 = {1}, p = {2:.16f}".format(argvs[1], argvs[2], 1.0))
          sys.exit()
  
      arg = sorted(map(int, argvs[1:3]))
      (sum_comb, comb, binary) = (1.0, 1.0, 0)
      for i in range(0, arg[0]):
          comb = comb * (arg[0] + arg[1] - i) / (i + 1)
          sum_comb += comb
          while (sum_comb > 1024): 
              sum_comb /= 1024; comb /= 1024; binary += 10
              
      p =  2 * sum_comb / 2 ** (arg[0] + arg[1] - binary)
      print("num1 = {0}, num2 = {1}, p = {2:.16f}".format(argvs[1], argvs[2], p))
  

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