Why are we weighting? The role of importance ratings in quality of life measurement.

Many Quality of Life (QoL) instruments ask respondents to rate a number of life domains in terms of satisfaction and personal importance, and derive weighted satisfaction scores by multiplying the two ratings. This paper demonstrates that this practice is both undesirable and unnecessary. QoL domains are selected on the basis of their inherent importance, rendering separate importance rating partially redundant. Weighted scores present difficulties in interpretation. Further, we show that multiplicative composites have undesirable psychometric properties. There is evidence that multiplicative composites have little or no advantage over unweighted ratings in correlational or predictive studies. Apart from the face validity and the intuitive appeal of multiplying satisfaction ratings by importance ratings, there appear to be no sound reasons for doing so, and several good reasons not to do so.