st: Unexpected Marginsplot Error Bars

[Alistair Windsor <alistair.windsor@gmail.com>]

For my wife's research we are running some zinb regressions. The 
indepvars for the inflate are a small subset of the total set of indepvars.
When we run the following commands

zinb depvar indepvars, inflate(indepvars) nolog iterate(20) robust 
cluster(ccode)
margins, predict(n)
marginsplot

we get a plot whose error bars stretch below 0. This seems impossible 
give that the negative binomial takes only non-negative values.
Am I missing something?

--
Alistair Windsor
Tigers Teach Co-Director and S-STEM PI
Assistant Professor, Department of Mathematical Sciences
355 Dunn Hall                             Ph:      901-678-4431
University of Memphis                Fax:    901-678-2480
Memphis, TN 38152-3240

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