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

1995). This form of measure may therefore be
described as using preference-based methods in
contrast to non-preference approaches, which
would describe many of the other types of instrument
we have already reviewed (Gold et al., 1996).
The former is concerned as far as possible to obtain
the respondent’s own overall value of the different
dimensions of his or her health status whereas the
latter, as has already been described, mostly derives
scores for dimensions of health status based on
summing responses to questionnaire items, with
the possibility of dimension scores being in
turn summed.
Utility measures therefore elicit the personal
preferences of individuals regarding health states.
This kind of measure has also been regarded as a
means of obtaining important evidence of the
overall value to society of health states. Data from
utility measures are applied to assess in turn the
social value of health care interventions by means
of cost–utility analysis (Patrick, 1976). Data regarding
costs and utilities for different health care
interventions have been used to inform decisions
about resource allocation between competing
interventions (Gold et al., 1996). Whilst most attention
has been given to utility measures because of
their role in cost–utility analyses to inform decisions
about resource allocation, there is some
research on their use as decision-aids in individual
patient care where patients face difficult choices
between treatment options (McNeil et al., 1982).
In the context of a clinical trial, there are two
basically different methods of assessing the preferences
or utilities of the patients involved. The most
direct way of assessing patients’ utilities associated
with health states is for them to be elicited directly
from patients who are in the health states of interest
by means of an interview in which respondents
take part in experimental tasks such as standard
gamble or time trade-off to elicit their values and
preferences (Read et al., 1984; Torrance, 1986,
1987; Drummond, 1987). In simplistic terms, the
experimental method employed with standard
gamble elicits respondents’ values regarding health
states by finding out how ready an individual would
be hypothetically to undergo varying levels of risk
associated with treatment to avoid a given health
state. The greater the level of risk acceptable to the
individual, the more severe the health state. The
analogous experimental task with time trade-off is
for subjects to judge the equivalence of periods of
time in a particular health state with varying shorter
periods in perfect health. The shorter the period
of perfect health considered equivalent, the more
severe the health state.
Health Technology Assessment 1998; Vol. 2: No. 14
The use of experimental tasks such as standard
gamble or time trade-off may be considered forms
of direct utility measurement in that patients in
a trial directly report their own values through
responses to experimental tasks in an interview.
Alternatively, utilities may be assessed by obtaining
information from the patients in a trial by means
of self-completed questionnaires that assess health
status more or less in the same way as other patientbased
outcome measures already reviewed. That is,
patients select items that most describe their health
state. However, in this second approach, questionnaire
items have weighted utility scores attached
that have been derived from prior survey data in
which utilities have been measured from, as far
as possible, appropriate samples of respondents
(Feeny et al., 1995; Brooks et al., 1996). This
second approach may be considered indirect
utility measurement in that whilst patients directly
report their health states, utility values attached to
these states are derived from prior research on the
preferences of other samples. A variant of indirect
utility measurement is to elicit values of a specific
patient group, say patients with arthritis, that can
then be used in other clinical trials of patients with
arthritis from whom it may not always be feasible
to perform full interviews.
It should be emphasised that the utilities approach
to patient-based outcome measures (whether considered
as a type of measure or as one form of
weighting the scores of measures) is distinctive in
the extent to which it draws on specific theoretical
assumptions. In particular the concept of utility
itself is central to utility measures. It is fundamental
to economic theory but, partly because of its
axiomatic status, it is hard to define (van Praag,
1993). Richardson (1994) refers to four different
concepts or uses employed by the literature when
referring to ‘utilities’. In one sense, it has been
used to refer to a psychological concept of wellbeing;
measurable levels of satisfaction and desirability
of individuals in relation to matters such
as health. A second usage refers to utility as the
ordinal ranking individuals have about options
such as health states. Thirdly, utility may be used
to refer to the intensity of preferences regarding
options. The fourth sense of the term refers to preferences
between options under conditions of risk.
These important differences of emphasis remain in
the current literature and cannot be resolved from
research evidence. A somewhat simplistic approximation
to the concept in the field of health states
that ‘the more ‘utility’ an individual expects to
obtain from a particular good or service the more
he will be willing to pay for it’ (Hurst and Mooney,
1983). However, willingness to pay is only a
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