Evaluating Patient-Based Outcome Measures - NIHR Health ...

Advantages and disadvantages
Several advantages are claimed for utility measures
over other forms of patient-based outcome assessments
(Bennett et al., 1991). Firstly, utility measures
provide a quantitative expression of the individual’s
values and preferences regarding overall health
status. The value to an individual of his health state
is here distinguishable from descriptions of different
aspects of that health state such as level of pain
or degree of immobility. A second, related advantage
is that a utility measure expresses one single
overall value for an individual’s preferences regarding
health. Utility measures require the integration
into one figure of the overall preference for a
health state, whereas typically health status
measures provide more multi-dimensional data
(Feeny and Torrance, 1989). A single summary
figure of health benefit is viewed as an advantage
particularly when comparisons and choices are
needed between the costs and benefits of different
treatments. For example, if a patient obtains some
relief from pain as a result of a treatment but as
a side-effect of treatment is made more tired or
depressed, this approach would aim to judge the
overall value to the patient of these experiences.
A third, and again related, advantage of utility
measures is that they are designed to provide
numerical values relative to states of perfect
health and death (Jette, 1980). This has the
consequence that outcome measures such as
the quality-adjusted life year (QALY) (Torrance,
1986), can be calculated as a single figure of
health benefit which numerically expresses on a
single continuum this full range of states. There
are other measures such as quality-adjusted time
without symptoms (Feldstein, 1991; Johnson,
1993), which are not considered to produce
utility measures as such, but do attempt a single
figure for health states. The argument for single
measures is that mortality and morbidity or
health status are otherwise incommensurable
making single expressions of health
benefit impossible.
Other advantages have been claimed for utility
measures which are less easy to test or inspect.
In particular, as has already been discussed, it
is argued that utility measures derive from a
‘rigorous theoretical foundation’ (Feeny and
Torrance, 1989). By comparison, many other
patient-based measures are atheoretical and
excessively pragmatic. A body of theory emerged
from the work of Von Neumann and Morgenstern
about the rational choices individuals make in
circumstances of uncertainty and risk (von
Neumann and Morgernstern, 1953). Methods
of experimentally identifying individuals’ utilities
Health Technology Assessment 1998; Vol. 2: No. 14
such as in standard gamble are considered robust
because they conform to the classic axioms of von
Neumann and Morgenstern (Gafni, 1994). However,
the axioms of rational choice are themselves
contested and much empirical evidence suggest
that individuals do not behave consistently according
to the axioms of decision theory (Sen, 1970;
Kahneman and Varey, 1991). Moreover the derivation
of measures of health utility from axioms are
difficult to demonstrate (Richardson, 1992). It is
therefore not easy to consider this a clear advantage
of utility-based approaches given the current
level of support for theoretical under-pinnings.
There are counterbalancing disadvantages (Feeny
and Torrance, 1989). Firstly there is a problem
with regard to feasibility. Interview based techniques
of eliciting preferences and utilities are
labour-intensive and time consuming (Torrance,
1995). Some respondents do not understand the
nature of the experimental tasks they are required
to perform. Well trained interviewers are therefore
needed. This problem of feasibility may be dealt
with by using questionnaire-based utility measures
such as EQ-5D because this instrument provides
indirect utility measures from prior evidence and
can be postally administered (Brooks et al., 1996).
EQ-5D is short and unlikely to impose the burden
on patients that direct elicitation of preferences via
an interview may impose. A second problem that
arises for indirect measures of utility, as for any
explicitly weighted health status measure such as
SIP or NHP, is that the value attached to any single
health state is a mean or median value around
which there is variance. The indirect value may
not reflect those of the individual patient being
assessed in a trial (Hadorn and Uebersax, 1995).
Thirdly, the principle of summarising preferences
by a single number is not universally accepted,
particularly when individuals’ preferences are
summed to produce a single figure for the social
value of an intervention (Drummond, 1992;
Spiegelhalter et al., 1992; Smith and Dobson, 1993).
It does not provide information on outcomes that
have an intuitive clinical meaning in the context
of a clinical trial, such as may be provided by an
expression of, for example, a particular percentage
reduction in pain or depression levels. By presenting
overall utilities in a single value, the direct
approach to the measurement of utilities cannot
provide the disaggregated evidence on specific
dimensions so that it cannot detect or express
contradictory trends in different dimensions of
outcome. Again, this problem may be overcome if
an indirect measure such as EQ-5D is used because
this questionnaire provides descriptions of five
different dimensions of health status.
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