Sample size to detect a significant difference between 2 proportions

Input Values


This utility calculates the sample size required to detect a statistically significant difference between two proportions with specified levels of confidence and power.

Inputs are the assumed true values for the two proportions, the desired level of confidence and the desired power for the detection of a significant difference and the desired ratio of sample sizes between the two groups. By default, calculations assume that a two-tailed statistical test will be used, but a one-tailed test can also be specified if preferred.

The program outputs the sample size required to detect the specified difference with desired power and confidence, for a one-tailed or two-tailed statistical test, as specified. Also output is a summary table of sample sizes for a range of assumed prevalence values.

Proportion in population 1:
Proportion in population 2:
Ratio of sample sizes (n2/n1):
Confidence level:
Desired Power:
Use 1 or 2-tailed test: 1 tailed
  2 tailed


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