Range and nummer-of-levels effects in derived and stated attribute importances

We study how the range of variation and the number of ttribute 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 allo,; 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.