# Comparison of proportions

## Description

Performs a Chi-squared test for the comparison of proportions observed in two independent samples. Proportions are expressed as a percentages.

## Required input

For both samples, you enter:

**Observed proportion (%)**: the observed proportion, expressed as a percentage.**Sample size**: the sample size or total number of observations in the sample.

## Results

The program calculates:

- the difference between the two proportions and a 95% confidence interval for this difference;
- Chi-squared test and P value.

If the P-value is less than 0.05, the conclusion is that the two proportions indeed differ significantly.

## Computational notes

SciStat.com 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, 2
^{nd}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.
- Richardson JTE (2011) The analysis of 2 x 2 contingency tables - Yet again. Statistics in Medicine 30:890.

## Link

Go to Comparison of proportions.