[R] P values

[Greg Snow]

Because if you use the sample standard deviation then it is a t test not a z test.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Thomas Roth
> Sent: Thursday, May 06, 2010 1:58 AM
> To: 'level'; r-help at r-project.org
> Subject: Re: [R] P values
> 
> Why
> 
> s = 1
> 
> ##
> 
> s = sd(A) #?
> 
> 
> -----Ursprüngliche Nachricht-----
> Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> Im
> Auftrag von level
> Gesendet: Mittwoch, 5. Mai 2010 22:41
> An: r-help at r-project.org
> Betreff: [R] P values
> 
> 
> How do u calculated p values for a z test..
> 
> so far i ve done this
> 
> A = read.table("cw3_data.txt")
> 
> xbar = mean(A)
> s = 1
> n = 20
> mu = 0
> 
> z.test = (xbar-mu)/(s/sqrt(n))
> 
> p.value = pnorm(abs(z.test))
> 
> error = qnorm(0.99)*s/sqrt(n)
> left = xbar - error
> right = xbar + error
> 
> and have got values off of it...but the values for p dont match up with
> other sites that i have used to check it agaisnt..such as wolfram alpha
> value i got was 0.7335039  when wolfram got 0.533.. any ideas where i
> ve
> gone wrong?  cheers
> --
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> Sent from the R help mailing list archive at Nabble.com.
> 
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