There are many different ways to measure pain and hence headache intensity. The methods that are most commonly used or applicable to clinical practice will be reviewed here.
Descriptive rating scales
A descriptive rating scale (DRS) usually consists of a series of pain descriptors from which patients choose the most accurate descriptor for their pain. A numerical value may be assigned to each descriptor. Examples of DRS (often referred to as verbal rating scales) for pain inten-sity and pain affect are given inFigure 13.2. For these the descriptors ‘none’ and ‘bearable’
would be scored as zero, ‘mild’ and ‘uncomfort-able’ would be scored as one, ‘moderate’ and
‘awful’ would be scored as two, and so on.
A DRS is usually easy to understand and use.
However, they may be relatively insensitive, which would necessitate large changes in order to reliably detect differences between testing. It cannot be assumed that there are equal spacings between ratings. For example, moderate (which would be given a value of two) is not necessarily twice as painful as mild (which would be given a value of one). Hence, they do not necessarily provide interval or ratio data so analysis of group data should be performed using non-parametric methods.
Numerical rating scales
A numerical rating scale (NRS) requires the patient to rate their pain on a defined scale.
For example, 0–10 where 0 is no pain and 10 is the worst pain imaginable (Fig. 13.3). Com-monly used NRS are 11 point (0–10), 21 point
Sensory:
Affective:
none bearable
mild uncomfortable
moderate awful
severe agonising
very severe excruciating
Figure 13.2Examples of descriptive rating scales for sensory and affective domains of pain.
Numerical Rating Scale – 101
Please complete on the line below the number between 0 and 100 that best describes your pain. A zero (0) would mean
“no pain” and a one hundred (100) would mean “pain as bad as it could be”. Please write only one number.
Box Scale – 11
Please put an X through the number that best represents your pain.
0 1 2 3 4 5 6 7 8 9 10
Figure 13.3Examples of numerical rating scales. A 101 numerical rating scale (above) and an 11 point box scale below.
(0–20) and 101 point (0–100) (Jensen &
Karoly 2001).Jensen et al (1996)used a 101-point scale on 124 chronic pain patients and found that 90–98% of patients used the scale in multiples of five (equivalent to a 21-point scale). Over 50% of subjects rated their pain in multiples of 10 (equivalent to an 11-point scale). They concluded that 11- and 21-point scales were sensitive enough to measure chronic pain. Kwong & Pathak (2007) found that an 11-point scale for measuring intensity of migraine was 55% more sensitive than a 4-point scale (none, mild, moderate, severe) in detecting clinically important differences.
Numerical rating scales may be administered verbally, where patients are asked to rate their pain and the therapist records the value. They may also be applied in written form, completed independently by the patient, either as a single rating or where the numbers are written in
ascending order and the patient is asked to cir-cle or select the number corresponding to their pain. Advantages of NRS are that they are eas-ily understood and quickly administered. They have been reported to be sensitive to change and correlate well with other pain intensity measures (Jensen & Karoly 2001). They do not appear to have ratio properties, meaning that a rating of 10, for example, does not nec-essarily indicate twice as much pain as a rating of five.
Visual analogue scales
A visual analogue scale (VAS) usually consists of a 100 mm line anchored at each end by descrip-tors (Fig. 13.4). Patients place a mark on the scale that corresponds to their pain. The dis-tance (usually in mm) from the lower end of the scale is then measured and recorded. Visual analogue scales are generally easy to understand
A: Place a mark on the line that best represents the usual intensity of your headache
Worst possible headache
B: Place a mark on the line that best represents the unpleasantness of your headache
Most unpleasant
pain imaginable
C: Place a mark on the line that best represents the change in your headaches since starting treatment
Completely better Not
unpleasant at all
No headache
Very much worse
No change
Figure 13.4Examples of visual analogue scales for measurement of: A¼ usual headache intensity, B¼ unpleasantness of headache pain, and C ¼ change in headaches.
and complete although 3–11% of patients may not be able to complete them (Ogon et al 1996). Patients have been shown to use all parts of the scale and no single point seems to be favored (Huskisson 1974). It is likely that the VAS is more sensitive than the DRS in detecting treatment changes (Jensen & Karoly 2001). The VAS can also be used to measure pain relief, treatment effect or change in con-dition, depending on the anchor descriptors (Fig. 13.4). The VAS correlates highly with descriptive and numerical rating scales and is thought to produce ratio data, at least for group measurements (Price et al 1983, Jensen &
Karoly, 2001). The VAS appears to be more reliable for current pain than remembered pains. In a series of 65 chronic low back pain patients.Love et al (1989)calculated reliability of present pain: r¼ 0.77, worst pain: r ¼ 0.49, and best pain: r¼ 0.57. Although not demon-strated on patients with headache, this point should be considered when asking patients to remember their headache intensity. A disadvan-tage of the VAS is that it is unidimensional.
Other dimensions have to be measured sepa-rately. Also, patients may not understand the requirements for completion, particularly if they have impaired cognitive function.
McGill Pain Questionnaire
The McGill Pain Questionnaire (MPQ) (Melzack 1975) was designed to reflect the sensory, affec-tive, and evaluative dimensions of pain. The MPQ contains 78 pain descriptors assigned to 20 categories within sensory, affective, evalua-tive and miscellaneous subclasses, a body chart, nine temporal adjectives and a ‘present pain index’ that is rated out of five. The descriptors are assigned an intensity value in each of 20 sec-tions, starting at one for the word with the least pain value. Scoring is via a Pain Rating Index (PRI) for each subclass and a total PRI. The number of words chosen and the score on the
PPI can also be used. The MPQ takes approxi-mately 5–10 minutes to complete once a patient has had some experience with it, but may take 15–20 minutes if they are unfamiliar with it (Melzack 1975). The MPQ may be read to the patient by the researcher/clinician or completed by patients themselves, although scores may be higher when the patient has the MPQ read to them (Klepac et al 1981). The construct validity of the MPQ has been reinforced by stud-ies that confirm the three-factor (sensory, evalu-ative and affective) structure (Lowe et al 1991, Turk et al 1985). The test-retest reliability or reproducibility of the MPQ has been calculated at 0.83 over ‘several days’ in 65 chronic low back pain patients (Love et al 1989). In a study of 16 patients with acute head pain after neuro-surgical procedure Hunter et al (1979) reported reproducibility over a five day period of greater than 0.89. It has been reported that the MPQ is sensitive to changes in pain related to various clinical syndromes (Melzack & Katz, 2001) although it does not appear to have been tested on benign, recurrent headache. The MPQ has been used widely for research but is clinically less practical due to the time taken to complete than other less complex scoring systems.
Short-form McGill Pain Questionnaire The Short-form McGill Pain Questionnaire (SFMPQ) was developed to provide an instru-ment that could be completed in less time than the MPQ but would still reflect both the sen-sory and affective dimensions of pain (Melzack 1987). The SFMPQ consists of 15 descriptors from the MPQ that were chosen by greater than 33% of patients with nine different pain syndromes including headache, low back pain, arthritis and dental pain. Of the 15 descriptors, 11 are from the sensory section of the MPQ and 4 are from the affective section. Each descriptor is ranked on an intensity scale of
0 ¼ none, 1 ¼ mild, 2 ¼ moderate and 3 ¼ severe. A VAS and a 0–5 numerical rating scale are also included. Scoring is by adding the rank-ings for the descriptors although sensory and affective descriptors may be scored separately (Melzack 1987). The VAS and numerical rating scale scores are not usually incorporated with the descriptor scores. The SFMPQ takes approx-imately five minutes to complete and score.
The SFMPQ was tested against the MPQ on 40 post-surgical, 20 obstetric, and 10 musculo-skeletal pain patients (Melzack 1987). The procedure was repeated for dental patients.
The results showed significant correlations (r¼ 0.65 to 0.93) between sensory, affective, and total scores for pre-and post-intervention scores. These results indicate that the SFMPQ may provide similar data to the MPQ on the dif-ferent dimensions of the pain experience, but in a more practical and timely manner than the longer version of the questionnaire.