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# Re: st: estimate 95%CIs of the mean for different sample sizes

 From Maarten buis To statalist@hsphsun2.harvard.edu Subject Re: st: estimate 95%CIs of the mean for different sample sizes Date Thu, 10 Jun 2010 03:42:50 -0700 (PDT)

```--- On Thu, 10/6/10, Miranda Kim wrote:
> I have data for a sample of 300 which is approximately
> normally distributed (slightly skewed). I would like to
> derive 95% confidence intervals around the estimate of the
> mean for sample sizes of 50, 80, 100, 150, and 400.
> Does anyone have any suggestions what command I can use to
> do this?

Here is one approach:

*----------------------- begin example ---------------------
program drop _all
*! version 1.0.0 MLB 10Jun2010
program define counterci, rclass
syntax varname [if] [in],  ///
n(numlist) [level(real `c(level)')]
marksample touse
qui sum `varlist' if `touse'
tempname se df lev res
matrix `res' = J(`: word count `n'', 2, .)
matrix rownames `res' = `n'
matrix colnames `res' = lb ub
local i = 1
foreach nobs of local n {
scalar `se' = r(sd)/sqrt(`nobs')
scalar `df' = `nobs' - 1
scalar `lev' = (100 - `level') / 200
matrix `res'[`i', 1] =                       ///
r(mean) - invttail(`df',`lev')*`se', ///
r(mean) + invttail(`df',`lev')*`se'
local ++i
}
matlist `res'
return matrix res = `res'
end

sysuse auto, clear
counterci gear_ratio, n(20 50 100)
*---------------------- end example --------------------------
(For more on examples I sent to the Statalist see:
http://www.maartenbuis.nl/example_faq )

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------

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```

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