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

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What are patient-based outcome measures?
This review is intended to be a resource with a
somewhat different purpose. It aims to provide
explicit guidance on how to select from the array
of available instruments. It makes as explicit as
possible the considerations relevant to choosing a
patient-based outcome measure for use in research.
It is primarily intended for use in the fields of
clinical trials and related evaluation studies where
a questionnaire assessing health status might be
included as a measure of outcome. This distinctive
focus is upon the assessment of changes in health
in groups of patients that may be detected in clinical
trials and may be due to the treatment under
investigation. Later in this chapter, other applications
of patient-based measures (in areas such as
health needs assessment and screening) are briefly
discussed, but a detailed consideration of other
uses is beyond the scope of this review. A number
of general discussions have already been published
with the intention of helping the trialist to select
and use patient-based outcome measures (Aaronson,
1989; Fitzpatrick et al., 1992; Guyatt et al.,
1993b; Guyatt, 1995; European Research Group
on Health Outcomes Measures, 1996; Testa and
Simonson, 1996). Guidance on choosing an
instrument has also been published in a number
of more specialist fields including; rheumatology
(Tugwell and Bombardier, 1982; Deyo, 1984;
Bombardier and Tugwell, 1987; Bell et al., 1990;
Fitzpatrick, 1993; Bellamy et al., 1995; Peloso et al.,
1995), cancer (Clark and Fallowfield, 1986;
Maguire and Selby, 1989; Moinpour et al., 1989;
Skeel, 1989; Fallowfield, 1993; Selby, 1993), cardiovascular
disease (Fletcher et al., 1987), neurology
(Hobart et al., 1996), surgery (Bullinger, 1991),
and in relation to particular applications such as,
drug trials (Jaeschke et al., 1992; Patrick, 1992)
and rehabilitation (Wade, 1988). This review
builds on and synthesises this body of literature.
It is intended to make as explicit as possible the
different properties that are expected of patientbased
outcome measures. They are presented in
terms of the criteria whereby we should judge
instruments when selecting the most appropriate
one for a particular trial. Where important differences
of views exist in the published evidence
on any point, the review attempts to reflect
this diversity.
Concepts and definitions
This is a review of a field in which there is no
precise definition or agreement about subject
matter (McDaniel and Bach, 1994). We are
concerned with questionnaires and related
instruments that ask patients about their health.
However with regard to more precise definitions
of what such instruments are intended to assess,
there is no agreed terminology and reviews
variously refer to instruments as being concerned
with ‘QoL’, ‘health-related QoL’, ‘health status’,
‘functional status’, ‘performance status’,
‘subjective health status’, ‘disability’, ‘functional
well-being’. To some extent, this diversity reflects
real differences of emphasis between instruments.
Some questionnaires focus exclusively upon
physical function, for example, assessing mobility
and activities of daily living without reference to
social and psychological factors, and might
appropriately be described as functional status
instruments. Other instruments may ask simple
global questions about the individual’s health.
Other instruments again are concerned with the
impact of health on a broad spectrum of the
individual’s life, for example, family life and life
satisfaction, and might reasonably be considered
to assess QoL. In reality the various terms such
as ‘health status’ and ‘QoL’ are used interchangeably
to such an extent that they lack real
descriptive value (Spitzer, 1987). It is unusual
in the current literature for terms such as ‘QoL’
to be selected with any specific intent. The term
‘patient-based outcome measure’ is here used
wherever possible as the most all-embracing term
to encompass all of the types of instruments
conveyed by other terms such as ‘health status’,
or ‘QoL’.
Some of the terms used to describe this field can
actually be unhelpful. In particular, the frequently
used phrase ‘QoL’ to describe instruments, misleadingly
suggests an abstract or philosophical set
of judgements or issues relating to life in the
broadest sense of factors outside the person, such
as living standards, political or physical environment.
Because, rightly or wrongly, hardly any of the
vast array of so-called QoL measures used in health
settings address matters beyond the health-related
(Meenan and Pincus, 1987), we avoid using this
terminology as much as possible.
The common denominator of all instruments
considered relevant to this review is that they
address some aspect of the patient’s subjective
experience of health and the consequences of
illness. Such instruments ask for patients to report
views, feelings, experiences that necessarily are as
perceived by the respondent (Mor and Guadagnoli,
1988). Respondents are asked about experiences
such as satisfaction, difficulty, distress or symptom
severity that are unavoidably subjective phenomena.
It has to be accepted that such experiences cannot
be objectively ‘verified’ (Albrecht, 1994). In some