I ran a ppmlhdfe regression on an unbalanced panel data looking at the citations received by individual sole-authored papers over time.
Then, to obtain the semielasticity, I run the following command, where dead_dumyA1 is a factor variable having two levels: equal to 1 if the author of a paper is dead in the particular year and 0 otherwise.
As shown by the output above, the command runs and provides me with the semielasticity, but I am worried about the following warning message:
“(note: continuous option implied because a factor with only one level was specified in the eydx() option)”
I cannot understand this message. Why is Stata saying that this factor variable has only one level?
I carefully checked this variable for the sample used in this regression, and there is no individual for which dead_dumyA1 is equal to 0 in all the years or all equal to 1 in all the years.
I am worried because a “continuous option implied” means that Stata is calculating a derivative, but I need the calculation of the discrete difference because " dead_dumyA1” is a factor variable with two levels.
I am using Stata MP 14.2.
Any help is greatly appreciated.
Code:
ppmlhdfe exclud_self i.paper_age i.dead_dumyA1 i.dead_dumyA1#c._2Year_citeAtDeath i.dead_dumyA1#c.AuthorActiveAtDeathRel 1.dead_dumyA1#c._2Year_citeAtDeath#c._2Year_citeAtDeath, absorb(i.paper) vce(cluster paper author_id) d
Then, to obtain the semielasticity, I run the following command, where dead_dumyA1 is a factor variable having two levels: equal to 1 if the author of a paper is dead in the particular year and 0 otherwise.
Code:
margins, eydx(i.dead_dumyA1)
As shown by the output above, the command runs and provides me with the semielasticity, but I am worried about the following warning message:
“(note: continuous option implied because a factor with only one level was specified in the eydx() option)”
I cannot understand this message. Why is Stata saying that this factor variable has only one level?
I carefully checked this variable for the sample used in this regression, and there is no individual for which dead_dumyA1 is equal to 0 in all the years or all equal to 1 in all the years.
I am worried because a “continuous option implied” means that Stata is calculating a derivative, but I need the calculation of the discrete difference because " dead_dumyA1” is a factor variable with two levels.
I am using Stata MP 14.2.
Any help is greatly appreciated.
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