Comparison of two proportions

Command

Tests Comparison of proportions

Description

Performs a Chi-squared test for the comparison of two proportions (from independent samples), expressed as a percentage.

This test is not performed on data in the spreadsheet, but on statistics you enter in a dialog box.

Note that when the total number of cases is less than 20, it may be more appropriate to perform Fisher's exact test.

Required input

In the dialog box, you can enter the two proportions (expressed as percentages) and the total number of cases.

For example when the prevalence of a disease in one sample of a total of 120 patients is 79%, and the prevalence of the disease in another sample of a total of 135 patients is 65%, you will enter the following in the dialog box:

After you click the Test button, the results of the test are displayed:

• the difference between the two proportions and a 95% confidence interval for this difference;
• Chi-squared test (with Yates' correction for continuity) and P value: when this P value is less than 0.05, the conclusion is that the two proportions indeed differ significantly.

In the Comment input field you can enter a comment or conclusion that will be included on the printed report.

Literature

• Altman DG (1991) Practical statistics for medical research. London: Chapman and Hall.