Create variable defining difference in mean

[Anders Schram]

Hi all,
I am trying to do an analysis indicating the difference between difference in mean scores (difference in difference analysis).
STATA has a option, though i find this difficult.

At this point I want to create a variable indicating the difference in mean score in my unpaired t-test.

I hope you can help me out

Sincerely,
Anders

[Carlo Lazzaro]

Anders:
welcome to this forum.
Do you mean something along the following lines?

. use "C:\Program Files\Stata17\ado\base\a\auto.dta"
(1978 automobile data)

. ttest price, unequal by(foreign)

Two-sample t test with unequal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. err.   Std. dev.   [95% conf. interval]
---------+--------------------------------------------------------------------
Domestic |      52    6072.423    429.4911    3097.104    5210.184    6934.662
 Foreign |      22    6384.682    558.9942    2621.915     5222.19    7547.174
---------+--------------------------------------------------------------------
Combined |      74    6165.257    342.8719    2949.496    5481.914      6848.6
---------+--------------------------------------------------------------------
    diff |           -312.2587    704.9376               -1730.856    1106.339
------------------------------------------------------------------------------
    diff = mean(Domestic) - mean(Foreign)                         t =  -0.4430
H0: diff = 0                     Satterthwaite's degrees of freedom =  46.4471

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3299         Pr(|T| > |t|) = 0.6599          Pr(T > t) = 0.6701

. return list

scalars:
              r(level) =  95
                 r(sd) =  2949.495884768919
               r(sd_2) =  2621.915083190759
               r(sd_1) =  3097.104279086425
                 r(se) =  704.937643377471
                r(p_u) =  .6700743053648903
                r(p_l) =  .3299256946351096
                  r(p) =  .6598513892702191
                  r(t) =  -.4429593797298984
               r(df_t) =  46.44711321147706
               r(mu_2) =  6384.681818181818
                r(N_2) =  22
               r(mu_1) =  6072.423076923077
                r(N_1) =  52

. g wanted=r(mu_1)-r(mu_2)

. list wanted in 1

     +-----------+
     |    wanted |
     |-----------|
  1. | -312.2587 |
     +-----------+

.