Apply these settings to all Share of Preference scenarios in this exercise
By default, all scenarios share the same Share of Preference settings. If you would like to use different settings for different scenarios, uncheck this option.
Limit Share of Preference to Top N Products per Respondent
The Share of Preference method allocates share to all products proportionally. When products are very similar, there is the potential for shares to be taken disproportionately from dissimilar products (the IIA problem, also known as the "red-bus/blue-bus problem"). When there is a large number of products and/or attributes, and performance from Randomized First Choice is slow, then you may want to use this technique to conduct Share of Preference simulations, but with reduced IIA problems. When enabled, shares of preference will only be allocated to the top N products (all others will receive zero share).
Let’s image that we were simulating choice among 80 competing automobiles in the marketplace. This would be a prime situation to experience IIA difficulties. The researcher might define N as 5, so for each respondent only the top five alternatives in terms of total utility capture a non-zero share of preference. The remaining 75 products receive zero share. Offering a new alternative (or improving an existing alternative) that a respondent really does not care much about will be unlikely to make any difference in the shares of preference for that respondent. You can see how this would reduce IIA.
The Top N setting for Share of Preference was introduced to our community by Kees van der Wagt at Sawtooth Software's 2014 Turbo Choice event, held in Amsterdam, The Netherlands.
When enabled, this number is the limit on how many of the top products will receive share.