st: mixlogit log normal distribution restriction problems

[Sorada Tapsuwan <sorada_tapsuwan@hotmail.com>]

Hi
I'm trying to estimate a mixlogit model and restrict a number of random variables to follow a lognormal distribution using the command ln(#).
However, when I ran the model it gave me an error message that says "Variables specified to have log-normally distributed coefficients should have positive coefficients in the conditional logit model. Try multiplying the variable by -1."
I have about 4 variables that have -ve coefficient values in the clogit model but none of them were significantly different from zero, so it's not like the coefficient is definitely -ve. So I figured that if I try to estimate them using mixlogit and restrict them to follow a lognormal distribution they should be okay but STATA doesn't like it. How can I then restrict these 4 variables to follow a lognormal distribution then?
Would anyone be able to help me with this problem. How can I overcome this constraint?
Thanks
S
 		 	   		  
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