Test Ologit Post

[Alan Neustadtl]

Using Stata V13 I am trying to 1) estimate an ologit model, 2) estimate marginal effects, and 3) plot the marginal effects. I include a factor variable for cohort or generation and a covariate measuring the year of the survey. When I use the margins command specifying both the factor variable and covariate, the margins look fine. But, when I plot the margins, one of the groups in the factor variable is not shown on the graph.

Here is the code from the ologit estimation:

. ologit conpressrev i.cohort1 c.year i.race

Iteration 0:   log likelihood = -27524.804
Iteration 1:   log likelihood = -26544.676
Iteration 2:   log likelihood = -26536.271
Iteration 3:   log likelihood = -26536.264
Iteration 4:   log likelihood = -26536.264

Ordered logistic regression                       Number of obs   =      27845
                                                  LR chi2(5)      =    1977.08
                                                  Prob > chi2     =     0.0000
Log likelihood = -26536.264                       Pseudo R2       =     0.0359

------------------------------------------------------------------------------
 conpressrev |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
     cohort1 |
    Boomers  |   .0969397   .0267096     3.63   0.000     .0445898    .1492896
      Gen X  |   .0987783   .0389694     2.53   0.011     .0223997    .1751569
Millennials  |   .3674232   .0737857     4.98   0.000     .2228059    .5120404
             |
        year |   -.047217    .001171   -40.32   0.000    -.0495121   -.0449219
             |
        race |
      black  |   .1088965   .0324684     3.35   0.001     .0452596    .1725333
-------------+----------------------------------------------------------------
       /cut1 |  -94.73947   2.328825                     -99.30388   -90.17506
       /cut2 |  -92.12877   2.324229                     -96.68418   -87.57337
------------------------------------------------------------------------------

And, here is an edited (shortened) listing of the margins:

. margins cohort1, at(year=(1973(1)2010)) predict(outcome(1))

---------------------------------------------------------------------------------
                |            Delta-method
                |     Margin   Std. Err.      z    P>|z|     [95% Conf. Interval]
----------------+----------------------------------------------------------------
    _at#cohort1 |
      1#Silent  |   .1684745   .0039917    42.21   0.000     .1606509    .1762982
     1#Boomers  |   .1553295   .0037288    41.66   0.000     .1480211    .1626379
       1#Gen X  |   .1550885   .0058258    26.62   0.000     .1436702    .1665068
 1#Millennials  |   .1230527   .0085103    14.46   0.000     .1063727    .1397326
      2#Silent  |   .1751917   .0040106    43.68   0.000     .1673311    .1830523
     2#Boomers  |   .1616245   .0037285    43.35   0.000     .1543167    .1689323
       2#Gen X  |   .1613756   .0058994    27.35   0.000      .149813    .1729382
 2#Millennials  |   .1282384   .0087473    14.66   0.000      .111094    .1453828
      3#Silent  |    .182118   .0040287    45.21   0.000     .1742219    .1900141
     3#Boomers  |   .1681239   .0037248    45.14   0.000     .1608233    .1754244
       3#Gen X  |   .1678669   .0059701    28.12   0.000     .1561657    .1795682
         .
         .
         .
     38#Silent  |   .5374293    .008247    65.17   0.000     .5212655    .5535931
    38#Boomers  |   .5132707   .0068983    74.41   0.000     .4997503     .526791
      38#Gen X  |   .5128115   .0078102    65.66   0.000     .4975038    .5281193
38#Millennials  |   .4458914   .0164728    27.07   0.000     .4136053    .4781775
---------------------------------------------------------------------------------

Note how there are margins estimate for all of the generation groups (Silent, Boomers, Gen X, and Millennials). So, I expect marginsplot to reflect all of these groups.

Here is the Stata code for the plot:

#d ;
marginsplot, recast(line) noci plotopts(lw(thick)) 
  title("Hardly any confidence") 
  xtitle("") ytitle("")
  ylabel(, format(%3.1f) angle(0))
  legend(row(1) region(color(none)))
  graphregion(color(white))
  name(conpressrev1, replace);
#d cr

I have attached a png graphic file showing how the Boomer generation is missing.

Any ideas on why this group would not be graphed?

Best,
Alan