01-25-2012 03:23 PM
I have a table below of comparing responses for the same question from a pre and post survey.
I want to know the 55.1% is statistically different from 42.5%.
I have no idea how to do this and have been stuck trying to figure this out. Any help you can give is appreciated.
|Table of survey by q15_both|
|Frequency Missing = 2|
01-31-2012 11:36 AM
I'm not an expert, but it sounds like you might want to look up McNemar's test, which is one of the tests for agreement.
For an example, see http://www.ats.ucla.edu/stat/sas/whatstat/whatstat.htm (search for "McNemar's Test" on the page)
input survey q freq;
0 0 27
0 1 22
1 0 17
1 1 23
proc freq data=a;
tables survey*q / agree;
/* or EXACT mcnem; for small samples */
01-31-2012 09:58 PM
Rick's right, McNemar's is the test for pre-post observations. The documentation talks about matched pairs, and pre-post is one kind of matching. It is testing whether the pairs that were 0-1 are different from the pairs that are 1-0, which is not quite the marginal test that you asked about initially. Be careful how you set it up; the sample size for McNemar's test is the number of pairs. In the table you show, it looks like you have broken the matching and have some missing data (N=49 for Post and 40 for Pre?).
If you cannot link the pre-observations to the post-observations, then you are back to the marginal test of homogenity that SusieQ pointed you to.