Scaling Conjoint Part Worths: Points vs. Zero-Centered Diffs
For over a decade, a re-scaling method called "Points" has been the default for reporting conjoint part worths (utilities) in Sawtooth Software's conjoint simulators. This approach gives equal weight to each respondent by making the total sum of part worths equal to the number of attributes times 100. Since conjoint part worths are scaled to an arbitrary constant within each attribute, it seemed to us early on that setting the worst level of each attribute for each respondent to zero was as reasonable a decision as any. This held promise of making it easier to present part worths to clients, since the values would generally fall in a comfortable range of about 0 to 100 (the values can actually exceed 100). However, we now suspect that fostering familiarity has sometimes led to misinterpretation. With the benefit of years of hindsight, we think that Points was a mistake.