Page 36 - The Importance of Common Metrics for Advacing Social Science Theory and Research

The Importance of Common Metrics for Advancing Social Science Theory and Research: A Workshop Summary
http://www.nap.edu/catalog/13034.html

24 THE IMPORTANCE OF COMMON METRICS

facilitate computing QALE over time. This would allow population track-
ing and measuring improvement in both survival and HRQoL over time.
He noted that there are several potential HRQoL indexes available today
9
that have been developed over the past 40 years, each with an associated
questionnaire varying from 5 to nearly 60 questions, with varying times to
completion from 2 to 15 minutes on average. All of these indexes conceive
of HRQoL as multidimensional, generally capturing physical, mental, and
social functions, as well as experience and feelings vis-à-vis some important
symptoms (e.g., pain, anxiety, depression). They all attempt to locate the
individual in a multidimensional health space; that multidimensional health
state is then scored by some sort of preference-based weighting function
based on population data.
The HRQoL indexes all differ. They use different dimensions, or they
conceptualize dimensions differently. They rely mostly on Guttman scales
or Likert scales to describe dimensions, but they use different categories,
different levels, and different numbers of categories. Their scoring functions
are based on utility assessments made by people sampled from the popula-
tions, but different populations and different econometric methods to elicit
these preferences are used. As a result, the indexes are related but different,
and each has flaws (e.g., differential coverage and differential sensitivity
among health domains, ceiling and floor effects), which may explain why
the United States has not adopted a standard HRQoL measure. Perhaps the
most contentious issue among the different indexes is where they place the
dead. Three of the scales have health states worse than dead.
In an effort to assess the different indexes and how they relate to a
common underlying latent scale of health, Fryback et al. (2010) used item
response theory in a novel way to put six of them on a common scale and
compare them. Two appeared linearly related, but the others showed ceil-
ing effects and therefore were not linearly related. The authors concluded
that these indexes are clearly not identical and are imprecisely correlated.
Fryback identified a number of other barriers to adopting a standard
HRQoL index for U.S. surveys:

• Competing developers and proprietary interests, which discourage
U.S. agencies from endorsing a measure that would create a finan-
cial winner and losers.
• The perceived large incremental response burden to add an entire
HRQoL questionnaire onto a national survey, when it can be chal-
lenging to add even one or two questions.

9 The indexes include the Quality of Well-Being scale, Self-Administered (QWB-SA), the
Health Utilities Indexes, the EuroQoL EQ-5D, the SF-6D, and the Health Activities and
Limitations Index (HALex).

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