[Limdep Nlogit List] Interaction between ASC and socio-economic variables

[F WD]

Dear all,

I am using a mixed logit model to estimate the preferences. In my model,
there are two types of alternatives and a status quo (alternative specific
constants). So basically, I had three utility functions. When I tried to
estimate the basic model without interaction with some socio-economic
variables, it works. However, When I tried to add the model with
interaction between ASC and socio-economic variables, it did not work. As
for your information, I use ASC to measure utility of status quo
alternative. I use dummy variable coding 1 if the respondent chooses the
status quo, and 0 otherwise. I want to know the effect of socio-economic
variable on the probability to opt “status quo”.

The syntax of mixed logit is below for basic model and it run well

RPLOGIT   ; Lhs = CHOICE ; Choices = 1,2,3

;model:

U(1,2) = PRICE*PRICE + X76*X76 + HANDLING*HANDLING + X62*X62 + X63*X63      +
LOCATION*LOCATION + X65*X65  +  QUANTITY*QUANTITY /

U (3) =  ASC + PRICE*PRICE + X76*X76 + HANDLING*HANDLING + X62*X62 +
X63*X63 + LOCATION*LOCATION + X65*X65 + QUANTITY*QUANTITY

; fcn = ASC(n), Price(c), X76(n), HANDLING(n), X62(n), X63(n), LOCATION(n),
X65(n), QUANTITY(n)

; Maxit = 50 ; Pts = 25 ; Halton ; Output = 3 ; Pds = 3 $



However, when I run to interact between ASC and some socio-economic
variables, it does not work.  I got the message: *Error   1027: Models -
estimated variance matrix of estimates is singular*

I use the syntax below:

RPLOGIT   ; Lhs = CHOICE ; Choices = 1,2,3

;model:

U(1,2) = ASC + PRICE*PRICE + X76*X76 + HANDLING*HANDLING + X62*X62 +
X63*X63 + LOCATION*LOCATION + X65*X65 + QUANTITY*QUANTITY +  AGE*ASCXAGE +
EDUC*ASCXEDUC + ORGANIC*ASCXORGA + RISKst*ASCXRISK + KTPA*ASCXKTPA +
COMMUNITY*ASCXKTCO /

U (3) = ASC + PRICE*PRICE + X76*X76 + HANDLING*HANDLING + X62*X62 + X63*X63
+ LOCATION*LOCATION + X65*X65 + QUANTITY*QUANTITY

; fcn = ASC(n), Price(c), X76(n), HANDLING(n), X62(n), X63(n), LOCATION(n),
X65(n), QUANTITY(n),

; Maxit = 50 ; Pts = 25 ; Halton ; Output = 3 ; Pds = 3 $



Does anyone know why the model in the interaction is not run? Is there any
wrong in the syntax? Thank you for your help.

best regards,
F