On Jun 22, 2009, at 7:56 PM, Jeffrey Edgington wrote:
Greetings,
I have two files which contain responses to a series of multiple
choice questions. One
file contains responses before an "intervention" and the other
contains the responses afterward.
There were three possible responses to each question: D, F, T (for
Don't Know, False, and True).
I would like to try McNemar's test to determine if there was any
significant difference between before
and after.
I read the files. I create tables using:
firstQuestion <- table( PreSurveyData$q1, PostSurveyData$q2)
The problem is that for several of the questions not all of the
possible responses appear. So I get
a table like this:
Missing cells added:
T D F
D 6 0 0
F 2 0 0
T 12 0 0
Which cannot be used in mcnemar.test because it is not a square
table and does not have enough rows and columns.
Is there some way to specify that R should count the occurrences of
D, F, and T even though they do not appear in the Data? Or some
easy way to add the missing columns?
You might want to exercise appropriate care regarding the validity
concerns, since you obviously have quite a few zero entries.
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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