From: Marc Schwartz <marc_schwartz_at_me.com>

Date: Fri, 22 Apr 2011 13:44:42 -0500

*>
*

*> data: xx
*

*> X-squared = 0.8425, df = 1, p-value = 0.3587
*

*>
*

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 22 Apr 2011 - 18:46:42 GMT

Date: Fri, 22 Apr 2011 13:44:42 -0500

On Apr 22, 2011, at 1:37 PM, John Sorkin wrote:

*>
*

> R 2.12

*> windows 7
**>
**> I am summary data that I would like to make into a 2x2 table representing counts positive vs. negative counts:
**> 28/289 20/276
**>
**> My table should look something like the following:
**>
**> group1 group2
**> Positive 28 20
**> Negative 289 276
**>
**> How can a (1) create the 2x2 table
**> (2) run a chi square test on the table?
**>
**> I have tried the following code, but I don't know if it is correct, and it does not give me an explicit 2x2 table:
**>
*

>> xx <- c(28,20) >> pp <- c(317/(317+296), 296/(317+296)) >> chisq.test(xx,p=pp)

>

> Chi-squared test for given probabilities

Hi John,

This is just a matrix. Thus, if you have the counts:

x <- matrix(c(28, 20, 289, 276), byrow = TRUE, 2, 2)

*> x
*

[,1] [,2]

[1,] 28 20

[2,] 289 276

> chisq.test(x)

Pearson's Chi-squared test with Yates' continuity correction

data: x

X-squared = 0.6491, df = 1, p-value = 0.4204

or as some might prefer:

# No Yates correction, which is conservative

> chisq.test(x, correct = FALSE)

Pearson's Chi-squared test

data: x

X-squared = 0.9141, df = 1, p-value = 0.339

**HTH,
**
Marc Schwartz

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 22 Apr 2011 - 18:46:42 GMT

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