[R] test of proportions

[Peter Ehlers]

You need to learn how to use prop.test properly.
Is this a ONE-sample test or TWO-sample test?

Perhaps this will help:

#"hand" calculation
phat <- 58/691
p <- 56/691
q <- 1-p
n <- 691
z <- (phat-p)/sqrt(p*q/n)
z
[1] 0.2787970
pnorm(-z)*2
[1] 0.7804006

#"prop.test"
prop.test(x=58, n=691, p=56/691, correct = FALSE)

         1-sample proportions test without continuity correction

data:  58 out of 691, null probability 56/691
X-squared = 0.0777, df = 1, p-value = 0.7804
alternative hypothesis: true p is not equal to 0.08104197

# Note the 'without' continuity correction part

  -Peter Ehlers

Roslina Zakaria wrote:
> Hi r-users,
> �
> I would like to use prop.test code and I also calculate manually to test the proportions for 2 groups.� The problem is the answer for the p-value�calculated manually are different from prop.test.� Here are the results:
> �
> ## Manually
> �
> z value: z= (phat-p)/sqrt(pq/n) = (.084-.081)/sqrt(.081(1-.081)/691)=0.289, pvalue=0.7718
> �
> 
> ## Using prop.test code 
>> low <- c(56,58)
>> tot <- c(691,691)
>> prop.test(low, tot, p = c(56/691,58/691), alternative = "two.sided", conf.level = 0.95, correct = TRUE)
> ������� 2-sample test for given proportions with continuity correction
> data:� low out of tot, null probabilities c(56/691, 58/691) 
> X-squared = 0.0096, df = 2, p-value = 0.9952
> alternative hypothesis: two.sided 
> null values:
> ��� prop 1���� prop 2 
> 0.08104197 0.08393632 
> sample estimates:
> ��� prop 1���� prop 2 
> 0.08104197 0.08393632 
> �
> �
> Thank you so much for any help given.
> 
> 
>       
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> 
> 
> 
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-- 
Peter Ehlers
University of Calgary
403.202.3921