[Limdep Nlogit List] Negative standard deviation of error component

[Lixian Qian]

Hello,

We are running an error component logit model with four alternatives.

SAMPLE ; All $
ECLOGIT; Lhs = Choice  ; Choices=CB,BL,CL,CS
    ;Model:
    U(CB) =Price*Capital + TripCost*TripCost+subsidy*subsidy + licen*licen + FCSERVICE*CSERVICE + FCTIME*TSERVICE + home*home + renew*recost/
    U(BL) =Price*Capital + TripCost*TripCost+subsidy*subsidy + licen*licen + BSERVICE*CSERVICE + BLTIME*TSERVICE + home*home + BL/
    U(CL) =RentCost*Cost + licen*licen+FCSERVICE*CSERVICE + FCTIME*TSERVICE + home*home + CL/
    U(CS) =ShareCost*TripCost + licen*licen + CSERVICE*CSERVICE + checka*checka+CS
    ; CheckData
    ; PTS=500
    ; ECM=(CB),(BL),(CL),(CS)
    ; PDS=4
    ; maxit=500
    ; Output = IC$

To our surprise, the results show that one error component has negative (and significant) standard deviation.

Can anyone please advise on the issue? Thank you.


Best,
Lixian