McNemar Test

Tap a term to see what it means, or .

Calculate

Example: 100 people said whether they approved of a project before and after a campaign. 30 approved both times, 35 disapproved both times, 10 switched to disapproving and 25 switched to approving. Did the campaign change opinions? Change the values to work out your own case.

Before × after table Row 1: before yes (after yes, after no). Row 2: before no (after yes, after no). Rows separated by a semicolon.

Step by step

What each term means

Chi-Square Statistic (χ²): Measures the imbalance between changes in the two directions. With 1 degree of freedom, it gives the p-value.
Difference of the Changes ((b − c)²): b is who changed from yes to no; c, who changed from no to yes. With no effect, the two would be similar.
Total Changes (b + c): Only the discordant pairs count: those who answered the same both times say nothing about change, however large that group is.

When to use it, assumptions and alternatives: the McNemar test in the statistical tests catalog.