[Rd] Confidence interval calculation in prop.test (PR#9325)
Duncan Murdoch
murdoch at stats.uwo.ca
Tue Oct 31 03:20:14 CET 2006
On 10/30/2006 8:50 PM, rmjohnston at mac.com wrote:
> Full_Name: Richard Johnston
> Version: 2.4.0
> OS: OS X
> Submission from: (NULL) (69.169.0.241)
>
>
> The confidence interval calculation for prop.test appears incorrect when
> alternative="greater" . The upper limit is always set to 1.0000. The lower
> limit appears to be correct.
That looks like a one-sided confidence interval, i.e. an interval of the
type Delta > 0.0369, where Delta is the difference in proportions. It
is then clipped to [-1, 1], since that's the largest possible range for
the difference.
What were you expecting to see?
Duncan Murdoch
>
>> total=c(250,250)
>> success=c(55,31)
>> prop.test(success,total,alternative="greater",correct=TRUE)
>
> 2-sample test for equality of proportions with continuity correction
>
> data: success out of total
> X-squared = 7.4289, df = 1, p-value = 0.003209
> alternative hypothesis: greater
> 95 percent confidence interval:
> 0.03693065 1.00000000
> sample estimates:
> prop 1 prop 2
> 0.220 0.124
>
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