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Logit analysis only possible on zero centered utilities?


I am using the anchored MDS utilities from the Sawtooth estimation module. In it, I get utility of anchor point as zero and the utility value of other attributes. But they are not centered to zero for each respondent.

So, when I calculate the choice likelihood using logit, should I zero center the utilities (excluding anchor point) or just use them as such.

In other words, when using logit analysis in MaxDiff, is it 100% necessary for the utilities to be zero-centered for each respondent?

asked Jan 27, 2014 by anonymous

1 Answer

+1 vote
As long as you are using "raw" utilities and not transformed or ZCD utilities, the logit choice rule will give you the same answer regardless of whether your utilities are zero-centered or not.  

You can prove this to yourself.  Consider utilities of 1 and 3 versus -1 and 1:  either way the product with the smaller utility gets a share of 12% and the one with the larger a share of 88%.
answered Jan 27, 2014 by Keith Chrzan Platinum Sawtooth Software, Inc. (90,475 points)