[Limdep Nlogit List] Scale parameter in RPL

[Emmanouil Mentzakis]

Hello,

I have data on the same DCE survey from two different samples and I
want to estimate a random parameter logit where I can allow for
differences in the scale. I know I can estimate an RPL with
heterogeneity in mean and heteroscedasticity in random parameters
using the -RPL- and -Hfr- options:

RPLOGIT
;Lhs = choice;Choices = alt1,alt2,none
;Halton
;RPL = sample2
;Fcn=X1(N), X2(N)
;Model:
U(alt1) = b1*X1 + b2*X2 /
U(alt2) = b1*X1 + b2*X2 /
U(none) = asc3
;Pds=6
;Hfr= sample2$

-sample2- is a dummy indicating the second sample.

However, I have seen in the literature RPL models (e.g. Hanley et al.
2005. Price vector effects in choice experiments: an empirical test.
Resource and Energy Economics) where they allow for differences in
scaling using just one parameter (i.e. scale); very similar to an
HLOGIT with the -Hfn=sample2- and -Sdv=1,1,1- options.

Could anyone please advice on how to estimate such RPL? Thank you in advance.

Best regards
Manos