stata experts,
I have been trying to find a way to store marginal estimations, including the p value and confidence interval.
Below is the code I have. All that I can get is the estimated marginal effect of variable I. Looks like I can't specify "ci" like what we can do for usual regression models. Is there a way to also store and present the other numbers from marginal estimations?
probit Y1 X
margin, dydx(X) post
est store m1
probit Y2 X
margins, dydx(X) post
est store m2
esttab m1 m2
esttab m1 m2, ci
Another related question is: how do I save marginal estimations for interaction terms? Example code below
probit Y2 year month year*month
margins year#month, asbalanced post
Thank you in advance!
Here's a way to grab p-values and confidence intervals after a margins command.
sysuse auto, clear
probit foreign price trunk
margin, dydx(price) post
eststo m1
The results from the margin command:
------------------------------------------------------------------------------
| Delta-method
| dy/dx std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
price | .0000268 .0000159 1.69 0.092 -4.36e-06 .000058
------------------------------------------------------------------------------
Then the p-value and confidence interval are recoverable from the stored matrices e(b) and e(V). To get the p-value, we need the z-score which is the point estimate over the standard error (e(b)[1,1]/sqrt(e(V)[1,1]). The rest is calculating the area in the two tails using normal.
The confidence interval is the point estimate e(b)[1,1] plus the standard error sqrt(e(V)[1,1]) times the critical value of z invnormal(0.975).
Shown with the output so that you can see the numbers line up:
. di "P-value: " normal(-abs(e(b)[1,1]/sqrt(e(V)[1,1])))*2
P-value: .09186065
. di "Upper bound: " e(b)[1,1] + sqrt(e(V)[1,1])*invnormal(0.975)
Upper bound: .00005796
. di "Lower bound: " e(b)[1,1] - sqrt(e(V)[1,1])*invnormal(0.975)
Lower bound: -4.361e-06
To put the p-value in a table, for example, you could use estadd:
estadd scalar pvalue = normal(-abs(e(b)[1,1]/sqrt(e(V)[1,1])))*2
And then esttab:
esttab m1, stats(pvalue, label("P-value"))
. esttab m1, stats(pvalue, label("P-value"))
----------------------------
(1)
----------------------------
price 0.0000268
(1.69)
----------------------------
P-value 0.0919
----------------------------
t statistics in parentheses
* p<0.05, ** p<0.01, *** p<0.001