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Abstract
We study how the range of variation and the number of attribute levels affect five measures
of attribute importance: full profile conjoint estimates, ranges in attribute level
attractiveness ratings, regression coefficients, graded paired comparisons, and self-reported
ratings. We find that all importance measures are affected by the range manipulation. The
number of attribute levels affects only two measures. The results allow us to benchmark the
magnitude of the number-of-levels effect against the range effect: conjoint importance
estimates were approximately equally affected by a threefold increase in the range of
attribute variation and by the insertion of two intermediate attribute levels. Our findings
show that the number-of-levels effect is most likely due to respondents’ tendencies to
distribute their mental stimulus representations and their responses uniformly over the
corresponding continua.