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The **margins** command (introduced in Stata 11) is very versatile with numerous options. This
page provides information on using the **margins** command to obtain predicted probabilities.

Let's get some data and run either a logit model or a probit model. It doesn't really matter since
we can use the same **margins** commands for either type of model. We will use **logit** with the binary
response variable **honors** with **female** as a categorical predictor and **read**
as a continuous predictor. Note that **female**, which is categorical,
is included as a factor variable (i.e. **i.female**) so that the **margins** command will
treat it as a categorical variable, otherwise, it would be assumed to be continuous.

We will begin our use ofuse http://www.ats.ucla.edu/stat/data/hsbdemo, clear logit honors i.female readIteration 0: log likelihood = -115.64441 Iteration 1: log likelihood = -87.616789 Iteration 2: log likelihood = -85.457393 Iteration 3: log likelihood = -85.443724 Iteration 4: log likelihood = -85.44372 Logistic regression Number of obs = 200 LR chi2(2) = 60.40 Prob > chi2 = 0.0000 Log likelihood = -85.44372 Pseudo R2 = 0.2612 ------------------------------------------------------------------------------ honors | Coef. Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- 1.female | 1.120926 .4081043 2.75 0.006 .3210558 1.920795 read | .1443657 .0233338 6.19 0.000 .0986322 .1900991 _cons | -9.603364 1.426412 -6.73 0.000 -12.39908 -6.807647 ------------------------------------------------------------------------------

You can ignore the part of the header that gives the mean formargins female, atmeansAdjusted predictions Number of obs = 200 Model VCE : OIM Expression : Pr(honors), predict() at : 0.female = .455 (mean) 1.female = .545 (mean) read = 52.23 (mean) ------------------------------------------------------------------------------ | Delta-method | Margin Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- female | 0 | .1127311 .0350115 3.22 0.001 .0441097 .1813524 1 | .2804526 .0509114 5.51 0.000 .1806681 .3802371 ------------------------------------------------------------------------------

We also get standard errors z-statistics and p-values testing the difference from zero and a 95% confidence interval for each predicted probability.

Next, we will use **margins** to get the predicted probabilities for the values of **read**
from 20 to 70 in increments of 10 while holding **1.female** at its mean. We will also
include the **post** option so that we can easily get the estimates and their standard
errors. We will also include the **vsquish** option to produce a more compact output.

The variablemargins, at(read=(20(10)70)) atmeans vsquish postAdjusted predictions Number of obs = 200 Model VCE : OIM Expression : Pr(honors), predict() 1._at : 0.female = .455 (mean) 1.female = .545 (mean) read = 20 2._at : 0.female = .455 (mean) 1.female = .545 (mean) read = 30 3._at : 0.female = .455 (mean) 1.female = .545 (mean) read = 40 4._at : 0.female = .455 (mean) 1.female = .545 (mean) read = 50 5._at : 0.female = .455 (mean) 1.female = .545 (mean) read = 60 6._at : 0.female = .455 (mean) 1.female = .545 (mean) read = 70 ------------------------------------------------------------------------------ | Delta-method | Margin Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- _at | 1 | .0022264 .0019625 1.13 0.257 -.0016201 .0060729 2 | .0093639 .0061007 1.53 0.125 -.0025934 .0213211 3 | .0385002 .0162829 2.36 0.018 .0065864 .070414 4 | .145024 .0311995 4.65 0.000 .083874 .2061739 5 | .4181148 .0498864 8.38 0.000 .3203393 .5158903 6 | .752714 .0670256 11.23 0.000 .6213462 .8840818 ------------------------------------------------------------------------------

An alternative way to view these results is as a graph that includes the predicted probabilities
along with the confidence interval. We will do this using a series of Stata matrix commands
followed by a **twoway** graph (note the lean1 scheme is available in gr0002).

mat t=J(6,3,.) mat a = (20\30\40\50\60\70) /* get the 6 "at" values */ forvalues i=1/6 { mat t[`i',1] = _b[`i'._at] /* get probability estimates */ mat t[`i',2] = _b[`i'._at] - 1.96*_se[`i'._at] /* compute lower limit */ mat t[`i',3] = _b[`i'._at] + 1.96*_se[`i'._at] /* compute upper limit */ } mat t=t,a /* horizontal concatenation */ mat colnames t = prob ll ul at /* fix column names */ svmat t, names(col) /* save matrix as data */ twoway (rarea ll ul at)(line prob at), legend(off) /// xtitle(read) ytitle(probability) scheme(lean1)

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