Statistical Methods – McNemar’s Test

What is McNemar’s Test?

The McNemar Chi-Square test is used in situations where data is not independent.

Specifically data is either matched (e.g. 2 people matched on similar characteristics, typically have different exposure – outcomes compared) or before-after data (e.g. one person measured before and after exposure – outcomes compared)

  • It is a non-parametric test
  • Tests the difference between paired proportions
  • Uses RAW numbers

Formulae… How to calculate McNemar’s test

  1. Data should be placed into a trusty 2×2 table
  2. As this is paired data, we will be ignoring concordant cells (a and d)
  3. Plug b + c numbers into the formulae above… et voila!

As with the Chi-Square test, the cut-off point for 95% significance level is 3.85 (which is 1.96 squared).  Therefore if the result is bigger than 3.85, we can say it is statistically significant at the 95% level (where p=0.05)

Here is a handy flow-chart to help decided which test to use.

…This was ‘borrowed’ from this useful website on commonly used statistical tests

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