The importance of 1st mentioned brand - a bit off topic

[Mark Webb-5]

Sorry-not specifically SPSS-but group may have ideas.
In brand purchase research it's common to ask 1st mentioned & other
mentioned.
e.g. A respondent has a total repertoire of 4 brands a,b,c,d and a is
the 1st mentioned and the order of mention of b,c,d are unknown.
I want to attach hypothetical probabilities to purchasing a brand. If I
didn't have a 1st mentioned I would make the probability of purchasing a
1/4 = 0.25 for any brand.
But I know that brand a is the preferred in a repertoire of 4 brands.
Is there any literature/academic publications that have addressed this
issue ?
i.e. as brand a is preferred it's probability is higher than 0.25 but by
what amount?

Would this amount change as the number of brands in the repertoire change ?

Regards

--
Mark Webb

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