This question comes from the design discussed in http://choice-metrics.com/forum/viewtopic.php?f=2&t=766. Since the topic is different, I open a new post.
I modified my design following Michiel recomendations, and decided not to use priors since I'm not positive that they are totally reliable. The design is:
- Code: Select all
Design
;alts = Car, Bike, Walk, None
;alg = swap(stop=total(5000 iterations))
;rows = 24
;block = 4
;eff=(mnl, d)
;cond:
if(Bike.lts_bike = 1, Walk.lts_walk = [1,2]) ,
if(Bike.lts_bike = 2, Walk.lts_walk = [1,2,3]) ,
if(Bike.lts_bike = 3, Walk.lts_walk = [2,3,4]) ,
if(Bike.lts_bike = 4, Walk.lts_walk = [3,4]),
if(Car.tt_car = 4, Bike.tt_bike = [4,5,6]), ?[(0%,25%,50%)]
if(Car.tt_car = 6, Bike.tt_bike = [6,8,9]), ?[(0%,25%,50%)]
if(Car.tt_car = 8, Bike.tt_bike = [8,10,12]), ?[(0%,25%,50%)]
if(Car.tt_car = 4, Walk.tt_walk = [8,9,10]), ?[(100%,125%,150%)]
if(Car.tt_car = 6, Walk.tt_walk = [12,14,15]), ?[(100%,125%,150%)]
if(Car.tt_car = 8, Walk.tt_walk = [16,20,22]) ?[(100%,125%,150%)]
;model:
U(Car) = b1 * tt_car[4,6,8] + ? I was using these priors [(u,-0.025, -0.0080)]
b2 * tc_car[0.5] +
b3 * pc_car[0,1,3] /
U(Bike) = b0 + b1 * tt_bike[4,5,6,8,9,10,12] +
b5 * lts_bike[1,2,3,4] /
U(Walk) = b00 + b1 * tt_walk[8,9,10,12,14,15,16,20,22]+
b7 * lts_walk[1,2,3,4]
$
The problem is the following:
- If I run this code, not using the priors indicated in the comment, all utilities are exactly 0 (and therefore the probabilities of the 4 alternatives = 25%).
- If I use the priors AND tt_car, tt_bike and tt_walk have the same generic coefficient, the utilities are not zero, but always utility car > utility bike > utility walk
- If I use the priors AND tt_car, tt_bike and tt_walk have specific coefficients, only the utility of car has a value, and the others are 0.
That also happens for the other two designs, which have the same structure but larger levels of attributes.
I wonder what can be wrong and would appreciate your help.