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How to code alternative specific linear price in simulation

I have some alternative specific linear price attributes and am using the sawtooth simulator. For the products where the linear price attribute doesn't apply typically i would code it as N/A on the front page, but here that results in an error. How should this be coded?
asked May 1 by Jackie
Are you using the standard desktop simulator, or an Excel saved version of the simulator?  The way you refer to "front page" suggests maybe you are using an Excel simulator?  Please clarify.
Hi Bryan, correct it's the excel based simulator

1 Answer

0 votes
OK, that makes more sense to me now that you say it is an Excel simulator.

The appropriate value to specify for an alt-specific attribute that doesn't apply to the current product concept is the same value that would have been coded during utility estimation for a not-applicable attribute.  That is zero.

Be careful when using Excel simulators generated out of our software with linear terms; that the values going into the design matrix linear terms were automatically zero-centered when estimating utilities via CBC/HB or via Lighthouse Studio.  So, you should continue to specify prices as zero-centered within your Excel simulator.  If you fail to do this, it will throw off the proper estimation of the None %.  The relative shares of preferences for the other product will be OK even if you've failed to do this.

For example, if you specified 1, 2, 3 for the prices for levels 1, 2, and 3 of a quantitative attribute (and you are using "Linear" coding rather than the default part-worth coding); our software automatically shifts those to -1, 0, +1 during utility estimation.  Thus, to specify your product in an Excel simulator afterward requires using -1 to refer to level 1, 0 to refer to level 2, and +1 to refer to level 3.  Otherwise, the None % will be wrong.
answered May 2 by Bryan Orme Platinum Sawtooth Software, Inc. (160,485 points)
Yes that's a good point- it looks like the excel simulator automatically zero centers them on the product coding page as long as you specify before exporting the simulator what the values should be.

For example I coded in both the analysis settings when I ran HB and also the attribute settings when exporting the simulator that p1=0.9, p2=1, p3=1.1, then in the excel simulator I can enter 0.9, 1, or 1.1 and on the product coding page it will zero center them automatically.

So from what you're saying, essentially there is no difference between an attribute being coded as the middle price point level in my case and it not applying because in both cases on the product coding page it will get a value of '0'. Does that sound right?
If you used 0.9, 1, and 1.1 for the three price points in the HB interface for Linear Pricing, then our software automatically would have shifted those values to be -0.1, 0.0, and 0.1 during utility estimation.  So, to obtain proper simulation results (for the None%), then you would need to use values from -0.1 to 0.1 when specifying prices in the simulator.

When the linear price attribute doesn't apply (assuming the price we're talking about is an alternative-specific price attribute), then you should specify a "0" as the price, which is the same specification as when the price is at the middle level.