Is it worth the weight? : revisiting weighted and unweighted scores with a quality of life measure

Subjective assessments of importance have been used as a weighting factor in measurement in a number of areas of research including quality of life, self esteem and job satisfaction. Despite the powerful intuitive appeal of this practice, conceptual and psychometric concerns with importance weighting have been raised, and research using weighted scores has produced mixed results. The advantages of importance weighting have therefore not been clearly established. The present study revisits importance weighting using data collected with the Injection Drug User Quality of Life Scale (IDUQOL). Weighted and unweighted IDUQOL scores from a subset of 241 participants from the Vancouver Injection Drug User Study (VIDUS) were correlated with measures of convergent and discriminant validity and a large number of criterion variables including drug use, stability of housing, involvement in drug treatment, and hospitalization. The contribution of importance ratings to scores on a global measure of life satisfaction was calculated using regression analysis. To determine whether importance ratings contributed significantly to the weighted IDUQOL total scores, analysis of variance was employed. Overall results of these analyses suggest that incorporating importance does not enhance the measurement of quality of life for this sample. However, the mean of satisfaction ratings for all important domains correlated significantly higher than the mean of satisfaction ratings for all unimportant domains with measures of convergent validity. It appears that the impact of importance depends at least in part on how it is measured and used. Further research may uncover methods for incorporating subjective importance that do increase the sensitivity of the IDUQOL and other quality of life measures.Education, Faculty ofEducational and Counselling Psychology, and Special Education (ECPS), Department ofGraduat