# What is the formula for share of preference scores in the online simulator?

Below is the explanation of what I'm seeing, and here is a link to a blinded file for reference/example:
https://www.dropbox.com/s/n5u8f4mt4q839td/Checking%20differences%20between%20calculations%20and%20online%20simulator%20-%20blinded.xlsx

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I am getting slightly different results when comparing a very basic Excel simulator and the online simulator with share of preference results.  My online simulator formulas are:

Total utility: The sum of all individual attribute level utilities, =SUM(C3,T3,AE3,AF3,BC3)

I did this for each of the 6 products in my simulation (I completely ignored the NONE product)

Share of preference: The antilog of product 1 divided by the sum of the antilogs of products 1 through 6, =EXP(BG3)/(EXP(\$BG3)+EXP(\$BH3)+EXP(\$BI3)+EXP(\$BJ3)+EXP(\$BK3)+EXP(\$BL3))

I've double and triple checked my formulas and even recreated it from scratch but I'm still getting different results.  I think there is an aspect of a formula I am missing.  It's probably simple, but I have never built an Excel simulator before.

Your formula sounds right.  But, make sure you're doing the share of preference computations for each respondent individually and then averaging the shares of preference across people.  Don't do it from average utilities.
answered Mar 18, 2013 by Platinum (148,340 points)

Yes, I am calculating these formulas at the respondent level and then averaging them.  But I am still getting different results.

I have posted a blinded version of my Excel file here in case it helps:

https://www.dropbox.com/s/n5u8f4mt4q839td/Checking%20differences%20between%20calculations%20and%20online%20simulator%20-%20blinded.xlsx
The online simulator defaults to the randomized first choice algorithm, which is different than the "share of preference" calculation.  You can edit a project and change the settings, I'm betting that's the issue.
Hi Brian,

That's not the issue either.  I had it set it to Share of Preference.  To confirm, I just changed it to Randomized First Choice and the numbers are different than the Share of Preference numbers.  See the comparison table below, where OS=Online simulator and XL=Excel.

SOP    SOP    RFC
XL    OS    OS
5%    5%    5%
20%    26%    27%
27%    25%    24%
20%    18%    20%
15%    14%    12%
14%    13%    11%

There must be some other issue.