R help - Oct 2008 - One-sample test for p

Hi, i am doing a statistics course and am having trouble with an exercise
where i need to determine whether my success rate at something is higher
than 80%. 
I was successful in 29 out of 60 trials, so these were the commands i
entered into R:
>n=60
>p.hat=29/n
>p.0=0.8
>se.0=sqrt(p.0*(1-p.0)/n)
>z=(p.hat-p.0)/se.0
>print(z)
Which returned:
[1] -6.132224
>1-pnorm(z)
Which returned
[1] 1

My problem is that i am meant to state a null and alternative hypothesis
which at the moment i have stated as  p>0.8 (null) and p?0.8 (alternative).
As things stand, though, a p-value of 1 suggests i should reject the null
hypothesis which can't be right since i am obviously successful less than
80% of the time. 
I am not sure where i am getting muddled. Any advice would be greatly
appreciated. Thanks!
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rr400 wrote:
> Hi, i am doing a statistics course and am having trouble with an exercise
> where i need to determine whether my success rate at something is higher
> than 80%. 
> I was successful in 29 out of 60 trials, so these were the commands i
> entered into R:
>> n=60
>> p.hat=29/n
>> p.0=0.8
>> se.0=sqrt(p.0*(1-p.0)/n)
>> z=(p.hat-p.0)/se.0
>> print(z)
> Which returned:
> [1] -6.132224
>> 1-pnorm(z)
> Which returned
> [1] 1
> 
> My problem is that i am meant to state a null and alternative hypothesis
> which at the moment i have stated as  p>0.8 (null) and p?0.8
(alternative).
> As things stand, though, a p-value of 1 suggests i should reject the null
> hypothesis which can't be right since i am obviously successful less
than
> 80% of the time. 
> I am not sure where i am getting muddled. Any advice would be greatly
> appreciated. Thanks!
This isn't really about R, and maybe it is homework, but now that we got 
you in the appropriate frame of mind:

(a) p values should look at "this or more unfavourable" events. You
have
arranged things so that that translates to -6.13 or _lower_. I.e. you're 
looking at the wrong tail.

(b) Make sure you get your accept/reject logic right. You _reject_ the 
null when data would be _un_likely if the null hypothesis were true.

(c) You might also want to play with binom.test and prop.test

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