Hello,

I have a model which is regressing log wages on being immigrant/native. However, immigrant are splitted into different arrival cohorts. Variables:
  • is051: 1 if immigrant, 0 if native
  • arrival: 0 if pre 1980 immigrant arrival, 1980 if immigrant 1980-84 arrival, 1985 if 1985-89 immigrant arrival, 1990 if 1990-94 immigrant arrival, 1995 if 1995-99 immigrant arrival, 2000 if 2000-04 immigrant arrival, 2005 if 2005-09 immigrant arrival, 2010 if 2010-14 immigrant arrival, 9999 if native;
  • age2=age^2, age3=(age^3)*(10^(-4))

My regression is:
Code:
svy: regress lnhourlyw_w c.age c.age2 c.age3    i.is051#c.age i.is051#c.age2 i.is051#
> c.age3 i.ib9999.arrival if year==2004
(running regress on estimation sample)

Survey: Linear regression

Number of strata   =         1    Number of obs     =     10,726
Number of PSUs     =    10,726    Population size   =  1,317,293
    Design df         =     10,725
    F(  12,  10714)   =     244.61
    Prob > F          =     0.0000
    R-squared         =     0.2189

    
Linearized
lnhourlyw_w       Coef.   Std. Err.      t    P>t     [95% Conf. Interval]
    
age    .1339665   .0152074     8.81    0.000     .1041572    .1637757
age2   -.0022769      .0004    -5.69    0.000    -.0030609    -.001493
age3    .1261596    .033307     3.79    0.000     .0608718    .1914474

is051#c.age
foreign     .1088957   .0338962     3.21    0.001     .0424529    .1753385

is051#c.age2
foreign    -.0024298   .0008359    -2.91    0.004    -.0040683   -.0007913

is051#c.age3
foreign     .1797601   .0657533     2.73    0.006     .0508716    .3086487

arrival
pre 1980    -1.962534   .4349641    -4.51    0.000    -2.815144   -1.109924
1980-84    -1.930812   .4371311    -4.42    0.000    -2.787669   -1.073954
1985-89    -1.942779   .4417473    -4.40    0.000    -2.808686   -1.076872
1990-94    -1.943912   .4435777    -4.38    0.000    -2.813407   -1.074418
1995-99    -1.743931   .4441677    -3.93    0.000    -2.614582   -.8732798
2000-04    -1.600682   .4372272    -3.66    0.000    -2.457728   -.7436355

_cons    1.260013   .1825067     6.90    0.000     .9022659     1.61776
I have to predict the the logwage at the age=40 for each immigrant cohort arrival and test the difference to that of natives. My idea looks like this:
Code:
predict    lnwage
(option    xb assumed;    fitted    values)
Code:
sum lnwage if arv2000==1 &    age ==40

Variable         Obs    Mean    Std.    Dev.    Min    Max
                    
lnwage          79    3.800933        0    3.800933    3.800933

. sum lnwage if is051==0 &    age ==40

Variable         Obs    Mean    Std.    Dev.    Min    Max
                    
lnwage         686    3.782984        0    3.782984    3.782984
Is there a way to test this difference? Do I have to store
Code:
sum lnwage if arv2000==1 &    age ==40
and
Code:
sum lnwage if is051==0 &    age ==40
and then test with
Code:
ttest
?