Statistical considerations for use of composite health-related quality-of-life scores in randomized trials.
Academic Article
Overview
abstract
BACKGROUND: Quality of life instruments are frequently used as outcomes in randomized trials. Instruments that consist of several subscales present researchers with a choice of whether to combine some or all scales into a single composite score. There may be several clinically and scientifically reasonable alternative combinations of subscales for the primary outcome measure. MAJOR FINDINGS: The statistical efficiency of different combinations of subscales depends on the relative effect size of the intervention on each subscale and the correlation between the subscales. Simple equations can be derived for determining the relative statistical efficiency of each clinically reasonable combination of subscales. Hypothetical scenarios show that the number of patients needed in a clinical trial can be twice as great for some combinations of subscales as for others. CONCLUSIONS: There are often compelling clinical or scientific reasons to use a particular subscale or composite in a randomized trial. In the case where a number of different alternatives would be reasonable, statistical efficiency can help guide the choice of endpoint.
