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  1. Commons Math
  2. MATH-1644

BinomialTest returns p-values > 1

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Details

    • Bug
    • Status: Resolved
    • Minor
    • Resolution: Fixed
    • 3.6.1
    • 4.0
    • None
    • None

    Description

       

      The code below produces the output "P-value for 10 trials, 5 successes, probability 0.5, two-sided alternative is 1.2460937500000002", but p-values should never be greater than 1. I think what is happening is that the test is adding both one-sided alternatives, but both include the 5 successes probability, so it is counted twice. This happens whenever the number of successes is exactly what is expected based on number of trials and success probability (numberOfSuccesses = numberOfTrials * probability).

      import org.apache.commons.math3.stat.inference.*;
      public class Main {
           public static void main(String args[]) {
              BinomialTest bt = new BinomialTest();
              Double pval = bt.binomialTest(10, 5, 0.5, AlternativeHypothesis.TWO_SIDED);
              System.out.println("P-value for 10 trials, 5 successes, probability 0.5, two-sided alternative is " + pval);
          }
      }
      

       

       

      Attachments

        1. patch
          2 kB
          Gilles Sadowski

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            Unassigned Unassigned
            wmchad Chad Young
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              Created:
              Updated:
              Resolved: