st: nlcheck - error: not sorted

[Barbara Engels <engels.ba@gmail.com>]

Dear Statalist,

testing for non-linearity, I conduct the nlcheck test, putting the the nlcheck command and the independent variable in question right after the  regression.Stata, however, tells me the independent variable is "not sorted" (although it is ; and after another "sort" it is still "not sorted). Can anybody help? Is nlcheck, after all, an appropriate test for checking linearity?

Best,
Barbara
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