While using the average of the tested prices to zero-center makes sense, we are wondering or trying to understand the affect of using 'average of tested prices' to zero-center when we want to simulate a non-tested price (i.e., an interpolated price). For example, if the prices are $2, $4, $6 & $8, the zero-centered values would be -3,-1,1,3. Now,if we want to simulate a price of $3, we'd use a zero-centered value of -1 to multiply the price utility. But,if we assume that $3 was also a price originally tested (shown to repsondents), then the zero-centered value would be -1.6 for $3.Thoughts please?

I guess I didn't put out my question properly in my earlier posting - so, the inclusion or exclusion of prices with in the price range changes the factor (in this example: -2 vs -1.6) that we need to multiply the coefficient with to get to the utility. How much does this difference in the factor affect the part-worth utility estimate for $3? I think, to start with, we can expect difference in the coefficient estimates because we are including an additional price point ($3) - but what role does the factor play in the final part-worth utility? In other words, is using zero-centering based on scanned values affecting results?