[R] a statistic question,a bit off-topic,but important

[Achim Zeileis]

On Wed, 20 Apr 2005 01:36:02 +0800 ronggui wrote:

> it seems that all the existing prop test assume 2 independent or
> matched sample.but in the real world, many situations are not as we
> assume.for example,i do a research on the voter's prefernce through a
> random sampling.and the sample shows that 23% of the sample choose
> A,28% choose B,the others choose C.and i want to test the diference
> between the proportion choosing A and B (23%-28%=-5%) is sinificant or
> just due to sampling error. i think the prop.test is not proper here.
> and it seems all the stat textbooks do not deal with these problem. is
> it a igorance in the statistical world or just something else?

If I understand you correctly, you're not interested in C at all and
just want to test P(A | C') = P(B | C') = 0.5. This can be done by
binom.test. Assuming the above were not proportions but observations
  binom.test(23, 23+28)
Instead of performing this exact test you can also perform the
asymptotic test via prop.test()
  prop.test(23, 23+28)
Z

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