Re: st: Question on Ttest.

[Richard Williams <Richard.A.Williams.5@nd.edu>]

Also, doing it the way you are doing it, I believe you could just multiply 
r(se) * square root of (N-1).  e.g. in this case, Stata would be doing the 
calculation .2387615526929942 * sqrt(127) = 2.690706.  (I know the logic of 
what to do, somebody who knows Stata better can probably figure out the 
exact commands!) RW

At 12:47 PM 11/21/2003 +0000, you wrote:

> Dear Statausers,
> I'm doing a simple ttest, however I would like to retrive the Std. Deviation
> of the difference of the means (see output below). Does anyone know if Stata
> saves this statistic?
> Many thanks,
> JP
>
>
> . ttest  match2291_0== match2291_1 if week>=2144
>
> Paired t test
>
> ----------------------------------------------------------------------------
> --
> Variable |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf.
> Interval]
> ---------+------------------------------------------------------------------
> --
> matc~1_0 |     127    76.95678    .9025185    10.17087    75.17072
> 78.74284
> matc~1_1 |     127    59.05176    .9798913    11.04281    57.11258
> 60.99093
> ---------+------------------------------------------------------------------
> --
>     diff |     127    17.90502    .2387616    2.690706    17.43252
> 18.37753
> ----------------------------------------------------------------------------
> --
>
>             Ho: mean(match2291_0 - match2291_1) = mean(diff) = 0
>
>   Ha: mean(diff) < 0         Ha: mean(diff) != 0        Ha: mean(diff) > 0
>        t =  74.9912                t =  74.9912              t =  74.9912
>    P < t =   1.0000          P > |t| =   0.0000          P > t =   0.0000
> r; t=0.18 12:41:07
>
> . return list
>
> scalars:
>               r(sd_2) =  11.0428143208466
>               r(sd_1) =  10.17086703109571
>                 r(se) =  .2387615526929942
>                r(p_u) =  1.0480080349e-106
>                r(p_l) =  1
>                  r(p) =  2.0960160698e-106
>                  r(t) =  74.99123715134762
>               r(df_t) =  126
>               r(mu_2) =  59.05175589013287
>                r(N_2) =  127
>               r(mu_1) =  76.95678011075718
>                r(N_1) =  127
>
> ----------------------------------------
>
> Joao Pedro W. de Azevedo
> School of Business (Economics)
> Ridley Building
> University of Newcastle
> NE1 7RU
> United Kingdom
>
> Telephone:  +44 (0) 191 222-5237
> Mobile: +44 (0) 7984-060675
> Fax:        +44 (0) 191 222-6548
> E-mail: j.p.azevedo@ncl.ac.uk
> http://www.students.ncl.ac.uk/j.p.azevedo/
>
>
> *
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-------------------------------------------
Richard Williams, Associate Professor
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*
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