Your approach tacitly assumes --- as did the poster's question --- that
the probability of passing an item by one method is *independent* of
whether it is passed by the other method. Which makes the methods
effectively independent of the nature of the item being assessed!
Not much actual quality being assured there!
cheers,
Rolf Turner
On 10/06/2008, at 2:57 PM, Greg Snow wrote:
here is one approach:
res <- cbind( c(10, 5, 1, 12, 3, 8, 7, 2, 10, 1),
c(90,15,79,38,7,92,13,78,40,9) )
line <- gl(5,1,length=10, labels=LETTERS[1:5])
qa <- gl(2,5)
fit <- glm( res ~ line*qa, family=binomial )
summary(fit)
anova(fit, test='Chisq')
The interaction terms measure the difference between the different
combinations of QA method and production line, if they are all 0,
then that means the effect of QA is the same accross production
lines and the qa main effect measures the difference between the 2
methods (allowing for differences in the prodoction lines), testing
if that equals 0 should answer your question.
Hope this helps,
________________________________________
From: [EMAIL PROTECTED] [EMAIL PROTECTED]
On Behalf Of Ivan Adzhubey [EMAIL PROTECTED]
Sent: Monday, June 09, 2008 4:28 PM
To: r-help@r-project.org
Subject: [R] Comparing two groups of proportions
Hi,
I have a seemingly common problem but I can't find a proper way to
approach
it. Let's say we have 5 samples (different size) of IC circuits
coming from 5
production lines (A, B, C, D, E). We apply two different non-
destructive QA
procedures to each sample, producing to sets of binary outcomes
(passed:
no/yes). So, we have two groups of proportions:
QA1 QA2
no/yes no/yes
A 10/90 8/92
B 5/15 7/13
C 1/79 2/78
D 12/38 10/40
E 3/7 1/9
How would I test if the two QA procedures in question give
significantly
different results, at the same time controlling for the possible
production
line contribution? It looks like there are many variants of multiple
proportions tests available in R and various extra packages but
none seems to
exactly fit this very simple problem. I would appreciate any advice.
Thanks,
Ivan
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