Hello,
I am working on an efficient design where the respondent has a statusquo and makes a choice between 4 alternatives (his status quo and 3 other alternatives) : Car, Public Transport , Bicycle and Walking. The alternatives are described by 4 attributes: time, cost, an individual preceived mobidity risk (physicalactivity) and a population morbidity risk(pollution).
I have 2 questions regarding the priors. I did not have time nor the budget to make a pilote, so I did a literature review and some personal assuptions to define the priors.
1- Through the literature review, I defined an interval of Value Of Time. From this interval I wanted to calculate the interval of the priors of time. I supposed that beta cost= -0,1 which allowed me to have the priors for time b1[(u,-0.05,-0.0017)]. At this level, wanting to introduce the priors for cost in my design I did not know what to do. Should I put a fixed prior b2[-0.1] following the assuption above? Or should I introduce an interval for this attribute giving ngene the information aout the sign that I am expecting for this attribute (for example a negative prior b2[(u,-0.1,-0.001)] for cost since higher cost is perceived negaively)? If It's an interval for priors of cost, should it be a large interval or a small one close to 0?
2- For the attributes about morbidity (physicalactivity and pollution), I could not find enough reliable sources to create an intervals of priors. The only information that I have is that the sign is negative (a risk of morbidity is perceived negatively). To express this information, I introduced negative priors b3[(u,-0.2,0)] and b4[(u,-0.2,0)]. Are these priors good enough for my situation? should I make the intervals larger or smaller?
Here is an example of my code for a respondent with a statuquo using the car:
Design
Design
;alts= Car, PT, Bicycle, Walk
;rows=21
;eff = (mnl,d)
;block=3
;model:
U(Car) = b1[(u,-0.05,-0.0017)]* Time.ref[4]
+ b2[-0.1] * Cost.ref[0.5]
+ b3[(u,-0.2,0)] * physicalactivity.ref[0.3]
+ b4[(u,-0.2,0)] * pollution.ref[0.3]/
U(PT) = b1* Time[5, 7, 9]
+ b2 * Cost[0 , 0.50 , 1.50]
+ b3 * physicalactivity[0.24, 0.26, 0.28]
+ b4 * pollution[0.27, 0.28, 0.29] /
U(Bicycle) = b1* Time[5, 6, 8]
+ b2 * Cost[0]
+ b3 * physicalactivity[0.24, 0.26, 0.28]
+ b4 * pollution[0.25, 0.26, 0.27] /
U(Walk) = b1 * Time[7, 10, 12]
+ b2 * Cost[0]
+ b3 * physicalactivity[0.20, 0.24, 0.27]
+ b4 * pollution[0.25, 0.26, 0.27]
$
Thank you in advance for your time and help.
Rim.