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# st: RE: Error message with predictnl

 From Nick Cox To "'statalist@hsphsun2.harvard.edu'" Subject st: RE: Error message with predictnl Date Wed, 8 Jun 2011 19:16:44 +0100

```Please study the following example:

. sysuse auto

. regress mpg i.foreign

Source |       SS       df       MS              Number of obs =      74
-------------+------------------------------           F(  1,    72) =   13.18
Model |  378.153515     1  378.153515           Prob > F      =  0.0005
Residual |  2065.30594    72  28.6848048           R-squared     =  0.1548
-------------+------------------------------           Adj R-squared =  0.1430
Total |  2443.45946    73  33.4720474           Root MSE      =  5.3558

------------------------------------------------------------------------------
mpg |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
1.foreign |   4.945804   1.362162     3.63   0.001     2.230384    7.661225
_cons |   19.82692   .7427186    26.70   0.000     18.34634    21.30751
------------------------------------------------------------------------------

. di _b[foreign]
[foreign] not found
r(111);

. di _b[1.foreign]
4.9458042

Similarly, in your analysis, -childfemale- appears in the guise of -1.childfemale-. Thus after model fitting there is no _b[childfemale] to refer to, but rather _b[1.childfemale]-.

Nick
n.j.cox@durham.ac.uk

Urmi Bhattacharya

I am running a logit model and I want to use the predictnl command to
get the predicted probabilities, the marginal effect of interaction of
two variables and so on along with the standard errors.

I do the following

logit school_left childage i.childfemale i.urban i.scstobc
i.casteother i.dadp i.dadm i.momp i.momm wagep wage5 wage8 wage9 distp
distm disth percapcons durat1 durat2 durat3 durat4 durat5 durat6
durat7 durat8 durat9 durat10 durat11, nocons nolog

Logistic regression                               Number of obs   =      47569
Wald
chi2(28)   =   14601.42
Log likelihood = -14502.393                       Prob > chi2     =     0.0000

------------------------------------------------------------------------------
school_left |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
childage |  -.1413654    .006069   -23.29   0.000    -.1532605   -.1294703
1.childfem~e |   .0212387   .0306462     0.69   0.488    -.0388266    .0813041
1.urban |   .0124911   .0368072     0.34   0.734    -.0596497    .0846319
1.scstobc |   1.972676   .1234074    15.99   0.000     1.730802     2.21455
1.casteother |   1.883233    .125722    14.98   0.000     1.636822    2.129643
1.dadp |    .680585    .044327    15.35   0.000     .5937057    .7674643
1.dadm |   .3872552   .0506982     7.64   0.000     .2878886    .4866217
1.momp |   1.351053   .0835161    16.18   0.000     1.187364    1.514741
1.momm |   .9494066   .0918146    10.34   0.000     .7694532     1.12936
wagep |  -.0281962   .0061845    -4.56   0.000    -.0403176   -.0160748
wage5 |  -.0040992   .0045604    -0.90   0.369    -.0130373     .004839
wage8 |    .021027   .0043869     4.79   0.000     .0124289    .0296251
wage9 |   .0159427   .0022335     7.14   0.000     .0115652    .0203203
distp |  -.0355589   .0162329    -2.19   0.028    -.0673748   -.0037431
distm |  -.0024083   .0112658    -0.21   0.831    -.0244888    .0196722
disth |   .0186932   .0039384     4.75   0.000      .010974    .0264124
percapcons |  -.0001459   .0000278    -5.26   0.000    -.0002003   -.0000915
durat1 |  -5.771466   .1406919   -41.02   0.000    -6.047217   -5.495715
durat2 |  -4.947835   .1222363   -40.48   0.000    -5.187414   -4.708256
durat3 |  -4.690019   .1193602   -39.29   0.000    -4.923961   -4.456078
durat4 |  -4.054464   .1132586   -35.80   0.000    -4.276447   -3.832481
durat5 |  -3.055883   .1082449   -28.23   0.000    -3.268039   -2.843727
durat6 |  -3.560284   .1130896   -31.48   0.000    -3.781936   -3.338633
durat7 |  -2.825943   .1099477   -25.70   0.000    -3.041436   -2.610449
durat8 |  -2.238741   .1094063   -20.46   0.000    -2.453173   -2.024308
durat9 |  -1.427979   .1099217   -12.99   0.000    -1.643421   -1.212536
durat10 |  -.3967904   .1152271    -3.44   0.001    -.6226313   -.1709495
durat11 |  -2.168164   .1486318   -14.59   0.000    -2.459477   -1.876851
------------------------------------------------------------------------------

Then I do

predictnl p_hat = (1+exp((-1)*(_b[childage]*childage
+_b[childfemale]*childfemale +_b[urban]*urban +_b[scstobc]*scstobc
+_b[casteother]*casteother +_b[dadp]*dadp +_b[dadm]*dadm
+_b[momp]*momp+ _b[momm]*momm+ _b[wagep]*wagep +_b[wage5]*wage5
+_b[wage8]*wage8 +_b[wage9]*wage9 +_b[distp]*distp +_b[distm]*distm
+_b[disth]*disth +_b[percapcons]*percapcons +_b[durat1]*durat1
+_b[durat2]*durat2
+_b[durat3]*durat3+_b[durat4]*durat4+_b[durat5]*durat5+_b[durat6]*durat6+_b[durat7]*durat7+_b[durat8]*durat8+_b[durat9]*durat9+_b[durat10]*durat10+_b[durat11]*durat11)))^-1,se(p_hat_se)

I get the error message saying
[childfemale] not found
r(111);

I am confused as to why I am getting this error message.

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```

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