The study findings suggest that the level of response involvement (high versus low) and the variability of product class quality (high versus moderate versus low) influence the size of the consumer’s choice set. By manipulating product class quality the authors show that as the variability in product class quality increases, consumers reduce the number of brands they will consider purchasing (evoked set) and increase the number of brands they won’t consider (inept set). They also use the response involvement variable a priori to categorize the (sample) population. The results indicate that, as the variability in product class quality increases, the high response involvement groups form smaller evoked sets and larger inept sets than the low response involvement groups.