Physiological measures

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Physiological measures
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Whether it is to examine the causes or consequences of pain or to evaluate the effectiveness of a treatment for pain, pain needs to be measured. This has raised several questions
and problems. For example: ‘Are we interested in the individual’s own experience of
the pain?’ (i.e. what someone says is all important), ‘What about denial or self-image?’
(i.e. someone might be in agony but deny it to themselves and to others), ‘Are we
interested in a more objective assessment?’ (i.e. can we get over the problem of denial by
asking someone else to rate their pain?) and ‘Do we need to assess a physiological basis
to pain?’ These questions have resulted in three different perspectives on pain measurement: self-reports, observational assessments and physiological assessments, which
are very similar to the different ways of measuring health status (see Chapter 16). In
addition, these different perspectives reflect the different theories of pain.
Self-report scales of pain rely on the individuals’ own subjective view of their pain level.
They take the form of visual analogue scales (e.g. How severe is your pain? Rated from
‘not at all’ (0) to ‘extremely’ (100)), verbal scales (e.g. Describe your pain: no pain, mild
pain, moderate pain, severe pain, worst pain) and descriptive questionnaires (e.g. the
McGill Pain Questionnaire (MPQ); Melzack 1975). The MPQ attempts to access the
more complex nature of pain and asks individuals to rate their pain in terms of three
dimensions: sensory (e.g. flickering, pulsing, beating), affective (e.g. punishing, cruel,
killing) and evaluative (e.g. annoying, miserable, intense). Some self-report measures
also attempt to access the impact that the pain is having upon the individuals’ level of
functioning and ask whether the pain influences the individuals’ ability to do daily tasks
such as walking, sitting and climbing stairs.
Observational assessment
Observational assessments attempt to make a more objective assessment of pain and
are used when the patients’ own self-reports are considered unreliable or when
they are unable to provide them. For example, observational measures would be
used for children, some stroke sufferers and some terminally ill patients. In addition,
they can provide an objective validation of self-report measures. Observational
measures include an assessment of the pain relief requested and used, pain behaviours
(such as limping, grimacing and muscle tension) and time spent sleeping and/or
Physiological measures
Both self-report measures and observational measures are sometimes regarded as
unreliable if a supposedly ‘objective’ measure of pain is required. In particular, selfreport measures are open to the bias of the individual in pain and observational
measures are open to errors made by the observer. Therefore, physiological measures
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