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

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What are patient-based outcome measures?
When the indirect method of assessing patients’
utilities is used, as has been explained, values
attached to health states are those obtained from
other more general samples. This has required the
use of statistical modelling to infer the values
attached to some of the possible states of health
described by such instruments because samples
have only been asked directly to value a core subset.
Adequacy of the modelling has been contested
(Brooks et al., 1996). Thus indirect methods may
not yet provide a complete set of directly elicited
values for all combinations of health states
(Rutten van Molken et al., 1995a).
Using instruments in combination
Before considering different applications of
patient-based outcome measures, it is helpful to
note a recommendation that has been made by
some authors that the optimal strategy is to use a
combination of types of measure in a clinical trial.
Most commonly it is recommended that trialists
include a generic together with a disease-specific
measure (Guyatt et al., 1991; Fletcher et al., 1992;
Bombardier et al., 1995). The main argument for
such an approach is that the two kinds of measures
are likely to produce complementary evidence,
with, for example, the disease-specific measure
producing evidence most relevant to the clinician
and also being most responsive to main effects
of an intervention while the generic measure
may produce information relevant to a broader
policy community (including those requiring
comparisons across interventions and disease
groups) and may also detect unexpected positive
or negative effects of a novel intervention. A
further refinement of this strategy is to include
a generic instrument with a disease-specific
measure as supplement, making efforts to ensure
that the disease-specific measure contains items
that minimally overlap with those of the generic
measure (Patrick and Deyo,1989; Patrick and
Erickson, 1993).
However, such a strategy cannot be recommended
without caveats. In the first place, the addition of
questionnaire items may impose a burden on
patients that reduces overall compliance. This
effect may be increased if respondents have to
answer items with overlapping content. The
repetitiveness that may attend such an approach
may appear insensitive on the part of investigators.
Secondly, the addition of each scale or instrument
increases the number of statistical analyses and
therefore significant effects arising by chance,
although this can problem can be managed by
disciplined identification of prior hypotheses.
A compromise strategy is to include a battery of
selected questionnaire items from different types
of measures, rather than whole scales. The clear
danger with this strategy is that items removed from
their context of whole instruments may not retain
the measurement properties (such as reliability
and validity) of the whole instrument, so that this
approach has least to recommend it.
Applications
As already stated, this text is intended to be a guide
in the use of patient-based outcome measures for
clinical trials. However, it is important to recognise
that such measures have been developed for a wide
range of different uses (Hunt, 1988; Fitzpatrick,
1994; Fitzpatrick and Albrecht, 1994). Some instruments
are considered to be applicable not just as
outcome measures in clinical trials but as instruments
that can also be used to assess the health
care needs of populations and assist health professionals
in assessing and caring for individual
patients. However insufficient attention has been
given to the different kinds of uses to which
instruments can be put (Sutherland and Till, 1993;
Till et al., 1994). This is a serious omission because
a questionnaire may have been established as
having considerable validity in, for example,
assessing health problems as a screening instrument
in hospital clinics whilst having less relevance
as a measure of outcome assessing changes in the
health status of the same patient group. The range
of alternative applications is briefly considered.
Clinical trials and cost–utility studies
The current review has been written with this
application in mind. There is far more agreement
about the potential and appropriateness of patientbased
outcome measures as endpoints in clinical
trials (Pocock, 1991). It is increasingly argued that
clinical trials should incorporate patient-based
outcome measures such as health status and QoL
except in circumstances where it is clear that these
issues are not relevant outcomes (Ganz et al., 1992;
Kaasa, 1992; Ganz, 1994). In some fields such as
cancer trials and surgery, thought has been given
to the circumstances when it is or is not relevant to
include such outcomes (Neugebauer et al., 1991;
Gotay et al., 1992; Hopwood, 1992; Nayfield et al.,
1992; Osoba, 1992). The clearest role for such
outcome measures is in the ‘gold standard’ form of
randomised controlled trial. Patient-based outcome
measures have been used as the primary outcome,
in randomised controlled trials, in a variety of fields
including cancer, rheumatology and heart disease.