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Multiple Sclerosis
Rating Scales for Clinical Studies in Neurology—Challenges and Opportunities
a report by
Jeremy Hobart, PhD, FRCP and Stefan Cano, PhD
Neurological Outcome Measures Unit, Peninsula College of Medicine and Dentistry, Plymouth, and Institute of Neurology, London
Rating scales are increasingly used as primary or secondary outcome Scale Cognitive Behavior Section (ADAS-cog) in dementia, despite
measures in clinical studies in neurology.
1
They are therefore becoming important limitations (further information available from authors).
the key dependent variables upon which decisions are made that
influence patient care and guide future research. The adequacy of these Second, statistical adequacy does not automatically confirm clinical
decisions depends directly on the scientific quality of the rating scales, validity or interpretability. An example from our own research focused on
which is reflected by the increased application of rating scale science probably the most widely used patient-reported fatigue rating scale
(psychometrics) in health outcomes measurement in neuroscience and (currently used in over 70 studies). We conducted two independent
increasing regulatory involvement by governing bodies such as the US phases of research. In the first phase, we carried out qualitative
Food and Drug Administration (FDA).
2,3
However, the majority of clinical evaluations of validity through expert opinion (n=30 neurologists,
studies in neurology that use rating scales are currently inadequate. Two therapists, nurses, and clinical researchers). The second phase involved a
simple examples illustrate some of the key issues. standard quantitative psychometric evaluation (n=333 MS patients). The
findings from the second phase implied that the fatigue measure in
First, current ‘state-of-the-art’ clinical trials in neuroscience continue to question was reliable and valid. However, the qualitative study in the first
use scales that have been proved to be scientifically poor. This is phase did not support either the content or face validity. In fact, expert
demonstrated through even the most superficial of literature reviews. For opinion agreed with the scale placement of only 23 items (58%), and
example, in a brief literature search in PubMed we identified randomized classified all of its 40 items as non-specific to fatigue (further information
controlled trials (RCTs) in multiple sclerosis (MS) published over a 20-year available from authors).
period (1987–2007). Of the 68 relevant articles, we found that 59% had
used a rating scale. However, only six (15%) of those articles had included Our research findings support the need for stringent quantitative and
scales that had any supporting psychometric evidence. This situation can qualitative requirements for rating scales used in neurology; such scales
be found throughout neurology and is further exemplified by the must also be proved to be clinically meaningful and scientifically rigorous
continued widespread use of the Rankin scale in stroke research, despite for valid interpretations of clinical studies. So, why is this not happening
growing concerns,
4
the Ashworth scale, despite its inherent weakness as right now? There are two key problems. First, the numbers generated by
a single-item scale (see below), and the Alzheimer’s Disease Assessment most rating scales do not satisfy the scientific definition for
measurements. Second, we do not really know what variables most
rating scales are measuring. This article addresses these two problems by
Jeremy Hobart, PhD, FRCP, is a Consultant Neurologist at Derriford
Hospital, Plymouth, and a Senior Lecturer at the Peninsula College
introducing some of the key issues in current rating scale research
of Medicine and Dentistry, Devon and the Institute of Neurology,
methodology. For readers who would like to learn more, we expand on
London. His clinical sub-specialist interest is the diagnosis and
these ideas in a recent review
1
and forthcoming monograph.
5
management of people with multiple sclerosis. His research
interest is rating scales for measuring health outcomes. He has
led the development of a number of rating scales, published over
Rating Scales as Measurement Instruments—
75 articles in this area, and is the recipient of numerous research
Some Basic Principles
grants. Dr Hobart completed his medical training at St Mary’s
Hospital Medical School, London, and the National Hospital
Before anything can be measured, the variable along which the
for Neurology, London.
measurements are to be made must be identified and marked out.
6
E: jeremy.hobart@pms.ac.uk
Common examples are rulers and weighing scales, which mark out length
in centimeters (or inches) and weight in grams (or ounces), respectively.
Stefan Cano, PhD, is a Chartered Psychologist and Lecturer in
Neurological Outcomes Measurement at the Institute of
They highlight three central features of all measurements, as illustrated in
Neurology, London, and at the Peninsula College of Medicine and Figure 1: first, instruments are constructed to make measurements;
Dentistry, Devon. He has published primary research, literature
second, the attribute being measured can be marked out as a line, or
reviews, and case reports in clinical and surgical journals across a
variety of health-related disciplines. He is a member of the British
continuum, onto which the measurements can be located; and third, the
Psychological Society. Dr Cano initially trained in psychology at markings on the continuum represent the units of measurement.
University College London, and later worked at the Chelsea and
Westminster Health Authority, London.
Variables such as height and weight can be measured directly.
Other variables—such as disability, cognitive functioning, and quality of
12 © TOUCH BRIEFINGS 2008
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