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Part-worth utility definition questions

Hello!

I have a simple question about part-worth utilities. The Lighthouse Studio manual indicates on page 367 that the "overall utility of any product is obtained by summing up the part-worth values of its specific attribute levels”. However it is my understanding that effects coding results in the average effect within each attribute as zero.

My question, then, is how - if the utilities sum to zero within each attribute with effects coding - how can the sum of the utilities for each attribute level equal the overall utility of that attribute?

Thanks!
asked Feb 5 by chelseav (190 points)

2 Answers

+1 vote
Chelsea - apples and oranges.  

The fist paragraph and the quote you show has to do with the total utility of a product (e.g. apple juice for $4 in a plastic container) wheres the second paragraph is about the sum of levels within an attribute (utility of apple juice is -1.25 and orange juice is +1.25 and their sum is zero).  

For the total utility of a product you'll never be summing all the levels of a particular attribute - in fact you'll be using just one level from each attribute, to the summing to zero business is irrelevant.
answered Feb 5 by Keith Chrzan Platinum Sawtooth Software, Inc. (77,550 points)
+1 vote
They don't. You are confusing product utility with attribute importance. A product's utility is found by summing the part worth utilities for one level from each attribute. Within each attribute they sum to zero, but across attributes using one level of each they usually don't sum to zero.

Importance scores, on the other hand, are measured by looking at the range of part-worths across the levels of an attribute. Though they sum to zero, the range (max minus min) will be non-zero even for binary attributes. The ranges can then be compared and percentages computed across attributes to find an "importance" for each attribute.
answered Feb 5 by Aaron Hill Gold Sawtooth Software, Inc. (10,195 points)
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