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Re: st: a question on t-test


From   "Lili Yan" <lyan16@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: a question on t-test
Date   Fri, 20 Jun 2008 16:38:58 -0500

Hi Richard,

Thank you very much for your prompt response! I did not use -ttest-
for several reasons:

First, I actually have a weight variale in my data and -ttest- does
not allow weights.
Second, I need compare means of many variables, so I want to quietly
run means calculation and comparison, then generate a table with -mat-
commands. In that table, I want to see p-value. So I have to calculate
it as Stata does not save it.

To me, the -lincom- seems to do what I want, but I want to confirm
this with people better in statistics and more familiar with Stata
than me. Please let me know if what I did is correct. Thanks a lot!

Best,
Lili



On Fri, Jun 20, 2008 at 4:24 PM, Richard Williams
<Richard.A.Williams.5@nd.edu> wrote:
> I'm probably missing something, but wouldn't it be a lot more
> straightforward just to use the ttest command, e.g.
>
> ttest mpg, by(foreign)
>
> At 04:57 PM 6/20/2008, Lili Yan wrote:
>>
>> Hi there,
>>
>> I need calculate the mean of two groups (say, native cars and foreign
>> cars) and do a t-test. However, I am not very sure if -lincom- is the
>> correct command after -mean-. Could anyone please let me know if the
>> following commands are right?
>>
>> mean mpg, over(foreign)
>> lincom [`var']0-[`var']1
>> di 2*ttail(r(df), abs(r(estimate)/r(se)))
>>
>> Thanks in advance!
>>
>> Best,
>> Lili
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>
> -------------------------------------------
> Richard Williams, Notre Dame Dept of Sociology
> OFFICE: (574)631-6668, (574)631-6463
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> EMAIL:  Richard.A.Williams.5@ND.Edu
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>
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