Inference for Proportions: Comparing Two Independent Samples

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Choose which calculation you desire, enter the relevant population values (as decimal fractions) for p1 (proportion in population 1) and p2 (proportion in population 2) and, if calculating power, a sample size (assumed the same for each sample). You may also modify α (type I error rate) and the power, if relevant. After making your entries, hit the calculate button at the bottom.

  • Calculate Sample Size (for specified Power)
  • Calculate Power (for specified Sample Size)
    • Enter a value for p1:
    Enter a value for p2:
  • 1 Sided Test
  • 2 Sided Test
    • Enter a value for α (default is .05):
    Enter a value for desired power (default is .80):
    The sample size (for each sample separately) is:

    Reference: The calculations are the customary ones based on the normal approximation to the binomial distribution. See for example Hypothesis Testing: Categorical Data - Estimation of Sample Size and Power for Comparing Two Binomial Proportions in Bernard Rosner's Fundamentals of Biostatistics.


    Rollin Brant
    Email me at: rollin@stat.ubc.ca