[R] Struggling to compute marginal effects !

[Willy Byamungu]

Dear Oscar,
and any other R-project person,

Can you please help me to figure out the meaning of the following error
message in red ?

Error in eval(predvars, data, env) :
  numeric 'envir' arg not of length one

I computed ordered logit models using 'polr' in R (I just followed the
guidance a handout I found on princeton.edu about logit, probit and
multinomial logit models) . The summary results are obtained without any
problem. *However*, when I'm using the package 'erer' to compute the
marginal effects for the ordered logit models, I'm just getting the error
message above.

Please HELP !!!!

Willy


-- 
Willy Mulimbi B.
AEAB Grad Student & Fulbright Scholar
Tel. (+1) 479-316-5981
Fayetteville, AR

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