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

For trialists selecting a patientbased
outcome measure
We recommend that, on as explicitly stated
grounds as possible, and making use of available
evidence about instruments, outcome measures
for clinical trials should be chosen by evaluating
evidence about instruments in relation to the
following eight criteria: appropriateness, reliability,
validity, responsiveness, precision, interpretability,
acceptability and feasibility. Although underlying
issues have been widely discussed, three of our
criteria, appropriateness, precision and interpretability,
are not always included in lists of desirable
properties of instruments. The remaining five
criteria are widely cited and identified in the
same or similar terminology as in this review.
The selection of instruments on the basis of our
criteria cannot, given the present state of the field,
be a straightforward or mechanical one. This is
partly because there is only a moderate level of
consensus about what exactly is meant by some
criteria. The literature does not provide unambiguous
definitions and advice regarding the issues
we have reviewed. The evidence for any given
instrument will be partial and complex to assimilate.
Above all, the criteria themselves cannot be
weighted or prioritised given the current state
of knowledge.
Investigators need to think of the desirable
properties of outcome measures for a specific
use in a specific trial question. Instruments do
not have properties of being reliable, valid and so
on in some universal sense; they are properties in
relation to a specific use. This makes selection of
instruments a complex process. Investigators need
to select outcomes appropriate to the question
addressed by a trial. Ideally each instrument is
optimally appropriate, valid, reliable and so on,
although, in reality, trials may include combinations
of outcome measures that together have
optimal measurement properties. There are costs
as well as benefits to be considered of following the
advice sometimes offered to include a combination
of generic and disease-specific measures.
Given the incomplete and complex state of
knowledge in this field, it may be advantageous
Chapter 5
Recommendations
Health Technology Assessment 1998; Vol. 2: No. 14
for investigators setting up trials to involve
those with expertise in outcomes in trial design
and analysis.
For developers of patient-based
outcome measures
To encourage more appropriate use of outcome
measures, those who develop such instruments
need to provide as clear evidence as possible of
the available evidence of new instruments in terms
of the eight criteria emphasised by this review.
Standards for documentation of patient-based
outcome measures will improve. These developments
will make the task in selecting outcome
measures for trials much more evidence-based.
Future research
In almost all areas reviewed there are substantial
gaps in knowledge and understanding of how
best to capture patients’ perceptions of illness
and outcomes of interventions within clinical
trials. There is therefore a strong case for further
methodological research in relation to patientbased
outcome measures. To facilitate appropriate
selection of instruments for clinical trials, two kinds
of further research in particular are needed. Firstly,
in trials and observational studies, the performance
of patient-based outcome measures should be
directly compared. There are still too few ‘head-on’
comparisons of different types of measures completed
by the same patients within a trial, especially
with regard to the issue of responsiveness. More
such studies are needed either in the form of
additional methodological components of major
clinical trials or as methodological investigations in
their own right. It will then be possible to address
questions such as whether disease-specific, generic
or other kinds of instruments are more responsive
in various clinical contexts. Secondly, researchers
and clinicians in specific areas, oncology, rheumatology,
psychiatry and so on, should carry out
assessments of evidence for the comparative
performance generally of the more widely used
of outcome measures in their field. This process
has begun to happen in some specialties and
publication of such consensus views would
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