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I have 400 patients and I apply 4 tests to all of them. This gives me a number of positive and negative for each test. I want to compare the tests 2 by 2 to find out if there is any statistically significant difference between them.

Test  Pos   Neg
1     100   300
2     150   250
3     160   240
4     200   200

What statistical test I can use to determine this? I'm very new to the field so I appreciate any pointers.

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4 Answers 4

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McNemar's test is the two by two comparison. NB You want to record for tests #1 & #2 how many patients tested +ve in both #1 & #2, how many +ve in #1 but -ve in #2, how many -ve in #1 but +ve in #2, & how many tested -ve in both #1 & #2.

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I was going to suggest the chi-squared test, but I think that your suggestion of McNemar's test would be better. A related topic would be the Fisher's exact test: https://en.wikipedia.org/wiki/Fisher%27s_exact_test.

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    $\begingroup$ From the example it looks like McNemar is what I need, but I'll keep Fisher in my mind too. There are just too many similar tests for a beginner to comprehend :) $\endgroup$
    – rslite
    Apr 8, 2013 at 23:25
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Perform a McNemar test for independence in a 2x2 table

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Paired proportions have traditionally been compared using McNemar's test but an exact alternative due to Liddell (1983) is preferable.

Useful links:

  • www.statsdirect.com/help/default.htm#chi_square_tests/mcnemar.htm
  • freesourcecode.net/matlabprojects/68089
  • jech.bmj.com/content/37/1/82.abstract
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  • $\begingroup$ There is an exact version of McNemar's test. $\endgroup$
    – gung - Reinstate Monica
    May 14, 2015 at 4:37

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