weak the sensations are and the temporal or spatial qualities of the sensations as
well the unpleasantness of the pain (Melzack and Torgerson 1971 ).
This chapter will briefly review how we can measure pain: what we have learned
from studies that require individuals to judge experimental pain stimuli such as that
associated with noxious heat (≥45 °C) or electrical shock stimulation; how mea-
sures of experimental pain stimuli are valid and also reliable for clinical pain
assessment; how experimental pain stimulation can be used to provide insights into
the onset and maintenance of persistent pain conditions; and how assessment of
nonverbal patient pain behavior as well as patient demographic factors influence
clinicians’assessment and management of clinical pain.
How do We Measure Pain?
Traditional pain measures have been used to either account for individual or group
differences in pain perception associated with experimental pain stimuli or to assess
individual differences in rating clinical pain. For the former measures, investigators
typically seek“benchmarks”for an individuals’pain experience. Thus, investiga-
tors may seek to determine pain threshold, the lowest level of stimulation that
subjects label to be reliably painful, or pain tolerance, the maximum level of
stimulation that subjects will tolerate. The dependent measures for these experi-
ences are measures of the stimulus magnitudes (e.g., °C for noxious heat temper-
atures or milliamperes of current for electrocutaneous electrical shock). However,
neither pain threshold nor pain tolerance measurement increases our understanding
of clinical pain with a magnitude that lies well within the lower bounds of threshold
and upper bounds of tolerance.
Reliable and valid pain measurement is important for effective clinical pain
management and is critical for clinical analgesic drug trials, for example, which
require measures that can temporally capture a patient’s pain ratings both before
and after the administration of putative pain reducing drugs and provide valid
assessment of changes in pain magnitudes. Further, clinical pain has traditionally
only been measured as a unidimensional experience. So, patients are requested to
rate their pain level on category scales,“none,”“weak,”“mild,”“moderate,”or
“severe”pain. The scales only provide a graded measure of pain; i.e., these mea-
sures provide relative ordering of pain levels, such that“moderate”pain is more
than“mild”pain and“severe”pain is more than“moderate”pain. For statistical
analyses, the categories are scored as the“none”=“0,”“mild”=“1,”etc., with
each increasing pain level ascribed the successive integer value. These scales have
measured differences in clinical pain relief between analgesic and placebo drugs
among those who have at least “moderate” pain at baseline. However, the
assumption that the category perceptions are equally spaced is not true (Heft and
Parker 1984 ). In fact, the increase in pain from“weak”to“mild”is roughly half the
increase from“mild”to“moderate.”
106 M.W. Heft and M.E. Robinson