Logical Decisions - Classweb

Logical Decisions - Classweb Logical Decisions - Classweb

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Different preference assessment methods have different traditions for deciding which goals should have a MUF. The Smart and Smarter methods often use a single overall MUF. The AHP approach generally has a MUF for each goal. The tradeoff and pairwise weight ratio methods can use either approach. Interactions apply to all the members of a MUF. If you want to have only a few particular members interact, you must include them in their own MUF. You should include members that interact under their own goal and make sure that that goal has its own MUF. In the discussions below we will call the members of a goal's MUF the "active members" for the goal. Representatives for Goals With a MUF. LDW will include goals that have their own MUF in the MUF for a higher level goal. Often it is difficult to answer preference assessment questions involving a goal because it is hard to interpret the meaning of different levels of utility for a goal. It may also be hard to remember the measures and sub-goals that are its active members and their importances. Therefore LDW allows you to select a representative for the goal in several weight assessment methods. The representative can be any measure below the goal in the goals hierarchy. It can also be any sub-goal with its own MUF below the goal in the goals hierarchy. The representative replaces the goal in the preference assessment questions for the MUF the goal is a member of. LDW computes the goal's weight based on the representative's weight in the MUF for the goal and the representative's weight in the MUF the goal is a member of. Here is a simple example. In the tutorial example, a "Performance" goal includes "Power" and "Fuel Economy" measures. The "Performance" goal and a "Price" measure make up the "Overall" goal (we'll assume that the "Styling" measure has been deleted). Suppose "Power" and "Fuel Economy" are assessed equal weights of 0.5 in the "Performance" goal's MUF. Now suppose that "Power" is selected as the representative for the "Performance" goal in the "Overall" goal's preference assessment. Suppose the "Power" and "Price" measures are also assessed equal weights of 9-34 Section 9 -- In Depth

0.5. Then the weight assigned to "Performance" will be 0.5 divided by the weight for "Power" in its MUF, which is also 0.5. This means that in the "Overall" goal's MUF, "Price" will have a weight of 0.5 and "Performance" will have a weight of 1.0. After LDW has adjusted these weights to sum to one, "Price" will have a weight of 0.33 and "Performance" will have a weight of 0.67. Note that LDW does not include the representative in the MUF instead of the goal it represents. The representative is just a tool that helps you define the weight that LDW should assign to the goal in the MUF it is a member of. For LDW to compute a goal's utility when only its representative's level has been defined, it must make an assumption about the utilities of the goal's other members. Therefore, when you define a goal LDW asks you to specify a nominal utility. LDW temporarily assigns this nominal utility to all of the goal's members, except its representative, when doing tradeoffs. This allows LDW to estimate the goal's utility as follows: U g(X r = x) = krU r(x) + k1U nom + ... + knUnom where = krU r(x) + (1 - k r)Unom U g(X r = x) = goal g's utility when its representative r has level x and the other members have the nominal utility, k r = the small k for the representative measure, U r(x) = the utility of level x for the representative measure, U nom = the nominal utility assigned to other members of the goal. LDW applies this formula recursively if the goal's representative is a member of a goal below it in the hierarchy. The formula is Section 9 -- In Depth 9-35

0.5. Then the weight assigned to "Performance" will be 0.5<br />

divided by the weight for "Power" in its MUF, which is also 0.5.<br />

This means that in the "Overall" goal's MUF, "Price" will have a<br />

weight of 0.5 and "Performance" will have a weight of 1.0. After<br />

LDW has adjusted these weights to sum to one, "Price" will have a<br />

weight of 0.33 and "Performance" will have a weight of 0.67.<br />

Note that LDW does not include the representative in the MUF<br />

instead of the goal it represents. The representative is just a tool<br />

that helps you define the weight that LDW should assign to the<br />

goal in the MUF it is a member of.<br />

For LDW to compute a goal's utility when only its representative's<br />

level has been defined, it must make an assumption about the<br />

utilities of the goal's other members. Therefore, when you define<br />

a goal LDW asks you to specify a nominal utility. LDW<br />

temporarily assigns this nominal utility to all of the goal's<br />

members, except its representative, when doing tradeoffs.<br />

This allows LDW to estimate the goal's utility as follows:<br />

U g(X r = x) = krU r(x) + k1U nom + ... + knUnom where<br />

= krU r(x) + (1 - k r)Unom U g(X r = x) = goal g's utility when its<br />

representative r has level x and the<br />

other members have the nominal<br />

utility,<br />

k r<br />

= the small k for the representative<br />

measure,<br />

U r(x)<br />

= the utility of level x for the<br />

representative measure,<br />

U nom<br />

= the nominal utility assigned to<br />

other members of the goal.<br />

LDW applies this formula recursively if the goal's representative<br />

is a member of a goal below it in the hierarchy. The formula is<br />

Section 9 -- In Depth 9-35

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