First off thank you providing this great forum to support usage of NGENE toolset.
I am developng a design for a SP study on the recovery of a threatened species.
There are three alternatives:
Status Quo, Option 1, Option 2
and three attributes for each alternative:
- population number
- time to recovery
- cost associated with option
Population number has 2 possible levels
Time to recovery attribute has 3 possible levels
Cost has 6 possible levels
Each respondent participating in the survey will be asked to complete three choice situations with varying attribute levels.
I am generating an WTP design with the following code:
- Code: Select all
Design
;alts = alt1*, alt2*, SQ
;rows = 36
;block=12
;eff = (mnl, wtp(ref1)) ;wtp = ref1(b1,b2/b3)
;cond:
if(alt1.fish >= alt2.fish and alt1.time <= alt2.time, alt1.cost > alt2.cost),
if(alt2.fish >= alt1.fish and alt2.time <= alt1.time, alt2.cost > alt1.cost)
;model:
U(alt1) = b1[0.0001]*fish[40000,70000] + b2[-0.04]*time[15,25,50] + b3[-0.01]*cost[40,75,120,200,250,300] /
U(alt2) = b1 * fish + b2 * time + b3 * cost /
U(SQ) = b4[0]
$
Note: the constraints need to included so that cost rises with increasing fish populations and/or decreased time to recovery.
I have the following questions:
1. Can I add additional contraints in NGENE so that within any given block, the respondent does not see the same combination of attribute levels at different prices. A colleague warned me that some respondents may get confused when the price varies for the same combination of attributes across choice scenarios. I'm not sure this will really be a problem, but I do remember a few of our focus group participants asking similar questions.
2. If it is not algorithmically feasible to have constraints within blocks, I may try to change levels manually.
Is this a bad idea? I realize this is not an NGENE question, but any guidance on this issue would be greatly appreciated.
If I do change them manually, I assume I can check the new design using the eval command.
thanks for any input.