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st: foreach command


From   "Elmer V Villanueva, MD ScM" <Elmer.Villanueva@med.monash.edu.au>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: foreach command
Date   Mon, 16 Jun 2003 09:21:22 +1000

Hi All!

The previous -for- command would do this:

.. for varlist var1 var2: ttest X, by(group)

->  ttest var1, by(group)

Two-sample t test with equal variances

------------------------------------------------------------------------
------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf.
Interval]
---------+--------------------------------------------------------------
------
Controls |      53    4.373019    .4801821    3.495779    3.409463
5.336575
   Cases |      52    6.741923    .7373028    5.316766    5.261726
8.22212
---------+--------------------------------------------------------------
------
combined |     105     5.54619    .4513336    4.624793    4.651179
6.441202
---------+--------------------------------------------------------------
------
    diff |           -2.368904    .8765335               -4.107302
-.6305068
------------------------------------------------------------------------
------
Degrees of freedom: 103

                 Ho: mean(Controls) - mean(Cases) = diff = 0

     Ha: diff < 0               Ha: diff != 0              Ha: diff > 0
       t =  -2.7026                t =  -2.7026              t =
-2.7026
   P < t =   0.0040          P > |t| =   0.0080          P > t =
0.9960

->  ttest var2, by(group)

Two-sample t test with equal variances

------------------------------------------------------------------------
------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf.
Interval]
---------+--------------------------------------------------------------
------
Controls |      39    .4102564    .1672108    1.044231    .0717559
..7487569
   Cases |      37    2.121622    .6984016    4.248211    .7051975
3.538046
---------+--------------------------------------------------------------
------
combined |      76    1.243421    .3619505    3.155412    .5223786
1.964463
---------+--------------------------------------------------------------
------
    diff |           -1.711365     .701359               -3.108853
-.313877
------------------------------------------------------------------------
------
Degrees of freedom: 74

                 Ho: mean(Controls) - mean(Cases) = diff = 0

     Ha: diff < 0               Ha: diff != 0              Ha: diff > 0
       t =  -2.4401                t =  -2.4401              t =
-2.4401
   P < t =   0.0085          P > |t| =   0.0171          P > t =
0.9915




The new -foreach- command does this:

Two-sample t test with equal variances

------------------------------------------------------------------------
------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf.
Interval]
---------+--------------------------------------------------------------
------
Controls |      53    4.373019    .4801821    3.495779    3.409463
5.336575
   Cases |      52    6.741923    .7373028    5.316766    5.261726
8.22212
---------+--------------------------------------------------------------
------
combined |     105     5.54619    .4513336    4.624793    4.651179
6.441202
---------+--------------------------------------------------------------
------
    diff |           -2.368904    .8765335               -4.107302
-.6305068
------------------------------------------------------------------------
------
Degrees of freedom: 103

                 Ho: mean(Controls) - mean(Cases) = diff = 0

     Ha: diff < 0               Ha: diff != 0              Ha: diff > 0
       t =  -2.7026                t =  -2.7026              t =
-2.7026
   P < t =   0.0040          P > |t| =   0.0080          P > t =
0.9960

Two-sample t test with equal variances

------------------------------------------------------------------------
------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf.
Interval]
---------+--------------------------------------------------------------
------
Controls |      39    .4102564    .1672108    1.044231    .0717559
..7487569
   Cases |      37    2.121622    .6984016    4.248211    .7051975
3.538046
---------+--------------------------------------------------------------
------
combined |      76    1.243421    .3619505    3.155412    .5223786
1.964463
---------+--------------------------------------------------------------
------
    diff |           -1.711365     .701359               -3.108853
-.313877
------------------------------------------------------------------------
------
Degrees of freedom: 74

                 Ho: mean(Controls) - mean(Cases) = diff = 0

     Ha: diff < 0               Ha: diff != 0              Ha: diff > 0
       t =  -2.4401                t =  -2.4401              t =
-2.4401
   P < t =   0.0085          P > |t| =   0.0171          P > t =
0.9915


Note that you lose any sense of what the dependent variable is. Instead,
the log simply lists t-test after t-test. Is there any way we can bring
back some marker of the command Stata repeats?





Thanks,


Elmer


************************************************
Elmer V Villanueva, MD ScM
Senior Research Fellow
Monash Institute of Health Services Research

Level 1, Block E
Monash Medical Centre
246 Clayton Road, Clayton
Victoria 3168 Australia

Tel:   (+61 3) 9594 7545
Fax:   (+61 3) 9594 7554
Mob:   0439 947 544
Email: Elmer.Villanueva@med.monash.edu.au
************************************************



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