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.

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.

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.

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).

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.