[R] CI with sd

[Petr Pikal]

Hi

On 19 Oct 2006 at 13:19, Ethan Johnsons wrote:

Date sent:      	Thu, 19 Oct 2006 13:19:40 -0400
From:           	"Ethan Johnsons" <ethan.johnsons at gmail.com>
To:             	"Chuck Cleland" <ccleland at optonline.net>
Copies to:      	r-help at stat.math.ethz.ch
Subject:        	Re: [R] CI with sd

> I thought of another interesting scenario, and I would just go ahead
> and ask this. I have a mean (i.e. 26.2) where the number of e coli
> samples is 250. The mean is already calculated, so it is a discrete
> value, not series.
> 
> What fucntion can be used for the calc with CI i.e. 90%?

With some sd value and assuming normal distribution

26.2+qnorm(.95)*sd/sqrt(250)
26.2-qnorm(.95)*sd/sqrt(250)

as you can find in statistical textbooks.

But without having sd value?

HTH
Petr


> 
> thx much,
> 
> ej
> 
> On 10/19/06, Chuck Cleland <ccleland at optonline.net> wrote:
> > Ethan Johnsons wrote:
> > > Please let me ask you another quick question.
> > > I have results for e coli, and am trying to get 95% CI with the sd
> > > (1.783956). I got the result from another tool as (1.21, 3.42).
> > > But, I like to verify it with R.  What function do you use for
> > > this?
> > >
> > >> e.coli=c(27.5,24.6,25.3,28.7,23,26.8,24.7,24.3,24.9)
> > >> sd(e.coli, na.rm = FALSE)
> > > [1] 1.783956
> > >
> > > Sorry for the newbie question.
> >
> > e.coli <- c(27.5,24.6,25.3,28.7,23,26.8,24.7,24.3,24.9)
> > library(nlme)
> > mod1 <- gls(e.coli ~ 1)
> > intervals(mod1)
> >
> > Approximate 95% confidence intervals
> >
> >  Coefficients:
> >                lower     est.    upper
> > (Intercept) 24.16206 25.53333 26.90460
> > attr(,"label")
> > [1] "Coefficients:"
> >
> >  Residual standard error:
> >    lower     est.    upper
> > 1.204986 1.783956 3.417651
> >
> > > thx much
> > >
> > > ej
> > >
> > > ______________________________________________
> > > R-help at stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide
> > > http://www.R-project.org/posting-guide.html and provide commented,
> > > minimal, self-contained, reproducible code.
> >
> > --
> > Chuck Cleland, Ph.D.
> > NDRI, Inc.
> > 71 West 23rd Street, 8th floor
> > New York, NY 10010
> > tel: (212) 845-4495 (Tu, Th)
> > tel: (732) 512-0171 (M, W, F)
> > fax: (917) 438-0894
> >
> >
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html and provide commented,
> minimal, self-contained, reproducible code.

Petr Pikal
petr.pikal at precheza.cz