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Logical Decisions - Classweb

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A: I could see where some people might think<br />

these were equally desirable, especially given<br />

what I've said before about these two measures,<br />

but I really think a truck should have balanced<br />

performance. I don't think I'd like to give up so<br />

much fuel economy to get really good power. So,<br />

I'd pick the balanced alternative B.<br />

Q: Good, that's the type of interaction I'm trying to<br />

get at here. Suppose I make alternative B less<br />

desirable. If I define B' as having 110 hp and<br />

getting 18 mpg, would you still prefer it to<br />

alternative A?<br />

A: No, now I think I'd prefer alternative A. I<br />

think I'd have trouble deciding if alternative B<br />

had 125 hp and got 19 mpg.<br />

LDW can combine this second tradeoff between power and fuel<br />

economy with the first one and the tradeoffs for the other<br />

members to compute the scaling constants for a multiplicative<br />

MUF formula. The algebra is somewhat complicated and won't<br />

be described here. The computations are all done automatically<br />

by LDW.<br />

You can make some qualitative checks on the computations,<br />

however. Since alternative B had levels that were less than the<br />

mid-preference levels, this means that the decision maker felt that<br />

the low level on MPG for alternative A had a relatively large<br />

effect on the overall utility. This corresponds to the third case in<br />

the table above (destructive interaction), where big K is greater<br />

than 0 and the small k sum to less than 1.<br />

i<br />

The response to a probabilistic question can also define the degree<br />

of interaction between two measures. Here LDW asks the<br />

decision maker to choose between two uncertain outcomes. This<br />

is the most difficult type of preference question used in LDW.<br />

You might pose the question as follows:<br />

Q: We already talked about the tradeoff between<br />

power and fuel economy. Now I want to look at<br />

those measures again to see if they have any<br />

interaction. Suppose a truck has uncertainties for<br />

some reason -- maybe it has an option package the<br />

dealer doesn't have the details for. Anyway, if you<br />

can imagine it, suppose the truck has a 50 percent<br />

9-60 Section 9 -- In Depth

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