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Compare Two Proportions Calculator

Use this free calculator to test whether two proportions (percentages) measured in independent samples differ significantly. Enter the proportion and sample size for each group; the calculator returns the absolute difference between the proportions, its 95% confidence interval, the chi-squared statistic, and the p-value.

Typical applications include comparing response or cure rates between a treatment and a control group in a clinical trial, checking whether a medical outcome differs between two patient populations, or analysing survey responses from two independent groups.

Example: Compare 45% (n=120) vs 60% (n=150).

 

Sample 1
: 
: 
Sample 2
: 
: 

Interpreting the results

Difference: the absolute difference in percentage points between the two proportions. A positive value means Sample 1 has the higher proportion.

95% confidence interval: the range within which the true difference in the population is likely to fall. If the interval does not include 0, the difference is statistically significant at the 5% level.

P-value: the probability of observing a difference at least this large by chance, assuming the two true proportions are equal. A p-value below 0.05 is conventionally considered statistically significant, though the actual threshold depends on the study context.

Computational notes

MedCalc uses the "N-1" Chi-squared test as recommended by Campbell (2007) and Richardson (2011).

The confidence interval is calculated according to the recommended method given by Altman et al. (2000).

Literature

  • Altman DG, Machin D, Bryant TN, Gardner MJ (Eds) (2000) Statistics with confidence, 2nd ed. BMJ Books. (p. 49)
  • Campbell I (2007) Chi-squared and Fisher-Irwin tests of two-by-two tables with small sample recommendations. Statistics in Medicine 26:3661-3675. PubMed
  • Richardson JTE (2011) The analysis of 2 x 2 contingency tables - Yet again. Statistics in Medicine 30:890. PubMed

How to cite this page

  • MedCalc Software Ltd. Compare Two Proportions Calculator — Chi-Squared Test | MedCalc. https://www.medcalc.org/en/calc/comparison_of_proportions.php (Version 23.6.2; accessed July 18, 2026)

Other free statistical calculators

See also

https://www.medcalc.org/en/calc/comparison_of_proportions.php

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