[R] significance in difference of proportions
Arne.Muller@aventis.com
Arne.Muller at aventis.com
Thu Nov 27 17:04:35 CET 2003
Hello,
I'm looking for some guidance with the following problem:
I've 2 samples A (111 items) and B (10 items) drawn from the same unknown
population. Witihn A I find 9 "positives" and in B 0 positives. I'd like to
know if the 2 samples A and B are different, ie is there a way to find out
whether the number of "positives" is significantly different in A and B?
I'm currently using prop.test, but unfortunately some of my data contains
less than 5 items in a group (like in the example above), and the test
statistics may not hold:
> prop.test(c(9,0), c(111,10))
2-sample test for equality of proportions with continuity correction
data: c(9, 0) out of c(111, 10)
X-squared = 0.0941, df = 1, p-value = 0.759
alternative hypothesis: two.sided
95 percent confidence interval:
-0.02420252 0.18636468
sample estimates:
prop 1 prop 2
0.08108108 0.00000000
Warning message:
Chi-squared approximation may be incorrect in: prop.test(c(9, 0), c(111, 10))
Do you have suggestions for an alternative test?
many thanks for your help,
+kind regards,
Arne
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