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A comparison of pain rating scales
Journal of Psychosomatic Research, Vol. 24. pp. 119 124 Pcrgamon Pres\ Ltd. 19RO. Printed I” Great Britam
A COMPARISON
OF PAIN RATING
ANTHONY (Received
E.
SCALES
READING
11 December
1979)
Abstract-In
the course of studying episiotomy pain in a small group of women (n = 26), a number of commonly used rating scales were compared. The results showed wide variation in the distribution of ratings between scales. Variation also emerged with respect to the degree of concordance between rating scale differences over time and subjective comparisons. The implications of these results are considered in terms of: (a) the way in which reliance on single rating scales may give rise to a misleading impression; and (b) the need to assess the various components of pain. Routine inclusion of multidimensional assessment methods is recommended. IN SPITE of advances in pain understanding and management, the assessment of the verbal report of clinical pain remains a difficult yet important task. Assessment may assist in diagnosis, thereby ensuring the appropriate treatment programme is selected. Similarly, evaluations of new treatment methods depend upon the availability of measures that reliably reflect fluctuations in the pain experience. A number of indices have been used: including rating scales [l], combinations of rating scales [2], cross modality matching [3, 41, questionnaires [5] and a card sort method [6]. Rating scales which focus on intensity only have been criticised owing to their failure to reflect adequately the multidimensional nature of pain [5]. Pain is a complex experience influenced by many factors in addition to the sensory input such as culture, emotions, psychological processes and reinforcement contingencies [7-91. There is evidence for two main dimensions of pain; sensory-discriminative and evaluative-emotional [lo, 111. The latter can be thought of as a flexible lens magnifying or reducing the amount of sensation that is felt. However, in spite of their limitations, self report scales-verbal, visual or numerical-have been the most commonly reported index [ 12, 131. It is apparent that more information is needed as to the adequacy and comparability of pain ratings scales, given their widespread usage. For example, where labels or anchor points are included, difficulties may result from the assumption that various complex definitions constitute a properly ordered scale. In fact, it is possible that patients may not be able to discriminate reliably between the points on the scale, and for some the points may not even be on the same dimension [ 141. The words supplied may also influence the distribution of responses, with anchor points determining where a non-uniform or uniform distribution of scores is obtained [12]. In the course of studying patient reactions to episiotomy a number of pain assessment scales were administered, permitting comparisons between different methods. Ratings were also made of specific pain adjectives reflecting both the sensory and evaluative components of pain. Three questions were addressed: (a) the correspondence between pain ratings on unidimensional rating scales; (b) the degree to which global ratings reflect specific aspects of the pain experience; and (c) the degree to which rating scales reliably reflect change over time. Senior Clinical Psychologist/Lecturer at the Department of Psychological Hospital Medical School, Denmark Hill, London SE5 8RX, U.K. 119
Medicine,
King’s
College
120
ANTHONY E. READING METHOD
A consecutive series of 26 women undergoing mediolateral episiotomy during childbirth were studied (mean age 24.6 yr; S.D. 5.3). All were fluent in English and had given birth to normal babies. None refused to take part in the study and all were told the assessments and interviews were for research purposes. The women were interviewed on successive days following delivery and at least 6 hr after receiving pain killing medication where this had been requested. On both occasions the episiotomy pain was assessed on a number of rating scales. These were: (a) the Present Pain Intensity (PPI) verbal rating scale [S], consisting of the adjectives “mild-discomforting-distressing-horrible-excruciating”: (b) a visual analogue rating scales (VAS) in the form of a 10 cm horizontal line with anchor points at both ends consisting of “no pain at all” and “worst pain imaginable”; (c) a IO-point horizontal numerical scale with verbal anchor points consisting of “none-mild-moderately distressing-very distressingunbearable”. In addition the quality of the pain was investigated by asking women to rate on 7 point scales a number of specific pain adjectives which were drawn from the McGill Pain Questionnaire (MPQ, [5]). Anxiety was assessed on the Spielberger State Trait Anxiety Inventory [15] and depression on IO-point ladder scales with 0 reflecting total depression and the top (10) completely happy.
RESULTS The mean scores on the three rating scales are shown in Table 1, along with Pearson product moment correlations between them. The means indicate a discrepancy between the PPI and the other two scales, with patients tending to score higher on the PPI. On the first day correlations were low, with only the association between the numerical scale and the VAS reaching significance (r = 0.46). The following day less variation in pain scores was evident, with correlations higher and all significant.
TABLE 1.-CORRELATIONS BETWEENPAIN RATINGSC-ZLESON EACH TESTINGOCCASION
Present
pain intensity
Visual analogue Numerical
scale
scale
day day day day day day
Mean
S.D.
3.3 4.3 27.2 19.5 4.0 2.9
(1.5) (1.1) (19.5) (15.5) (2.0) (1.7)
1 2 1 2 1 2
Visual analogue 0.29 (0.711_)
scale
Numerical
scale
0.26 (0.57*) 0.46t
(0.62-t)
Day two correlations in parentheses. *P< 0.05; fP< 0.01.
Correlations were also computed between global ratings and individual quality ratings on the adjective checklists and are presented, with mean ratings for each adjective for each day, in Table 2. It can be seen that the following words were used to describe the postepisiotomy pain on both assessment occasions: “throbbing, cramping, pulling, stinging, aching, tiring and annoying”. Pearson product moment correlations were higher on the second day postpartum. On day 1 no significant correlations emerged between the PPI and individual pain descriptors. Two words correlated significantly with the VAS score (pulling: r = 0.37; and throbbing: r = 0.52). On the second day, the VAS was significantly correlated with 5 words reflecting the sensory qualities of the pain (throbbing, shooting, stabbing, cutting and burning). In contrast, the majority of adjectives correlated significantly with the numerical rating scale scores.
A comparison
121
of pain rating scales
TABLE~.--MEANRATINGS~NADJECT~VESANDC~RRELAT~~NSW~THGLOBALRAT~NGSCALESFORBOTHTEST~NG OCCASIONS
Rating scale Mean score Pain adjective
I
day
Throbbing Shooting Stabbing Cutting Cramping Pulling Burning Stinging Aching Tiring Sickening Terrifying Punishing Annoying Unbearable *P< 0.05; fP<
1.7 1.2 1.3 1.4 1.4 1.6
1.o 1.9 3.0 1.4 1.3 0.3 0.8 2.7 1.2
Present
pain intensity
Numerical
Visual analogue
day 2
day 1
day 2
day 1
1.5 0.4 0.7 0.7 1.3 2.0 0.6 1.6 2.0 1.2 0.5 0.7 0.1 1.5 0.2
0.00 0.25 0.21 0.17 0.22 -0.02 0.12 0.22 0.16 0.15 0.12 0.29 0.06 0.06 0.21
0.51* 0.23 0.19 0.39 0.43 0.41 0.13 0.16 0.31 0.11 0.20 0.10 -0.23 0.47” 0.15
0.52t 0.06 -0.06 0.04 0.09 0.37* -0.07 0.07 0.13 0.02 -0.05 0.11 -0.01 0.16 0.06
I
day 2
day
0.70-f 0.78-f
0.63-t
0.50* 0.62t 0.33 0.42 0.55t 0.26 0.41 0.13 0.21 0.72t -0.14 0.15 0.27
0.62t
0.61t 0.61t 0.46t 0.72t 0.52t 0.49t 0.55t 0.51t 0.69t 0.62t 0.43* 0.43* 0.70t
day 2 0.42 0.39 0.54* 0.69t 0.34 0.71t 0.72T 0.63t 0.83t 0.40 0.68$ 0.25 0.46* 0.61t 0.52*
0.01.
In order to assess the sensitivity to change of each of the scales, the differences between ratings on day 1 and day 2 were computed. These were compared with responses to the question “how does the pain you are now experiencing compare with the one at the time of the assessment yesterday?” Of the sample of 26 women, only 19 were experiencing sufficient pain at the time of the second interview to complete the scales. Answers to this question were translated into greater, same or less and kappa coefficients of agreement were computed between these subjective comparisons and the computed rating score differences. The results are shown in Table 3 for each of the pain rating scales. Ideally, with high concordance, the majority of patients would fall in the top-left to bottom-right diagonal. As shown in Table 3, there was a wide distribution with some women reporting less pain and yet achieving higher scores on the rating scales. The highest kappa coefficient was found for the VAS (0.47), with 11 of the sample lying in the diagonal. Lower levels of agreement were found for the numerical and PPI scales. TABLE ~.--CORRESPONDENCEBETWEENGLOBALCOMPARlSONSANDCOMPUTEDRATlNGSCALEDlFFERENCES
Global comparisons Rating scale
Less
Same
More
Present pain intensity
Less Same More
0 0
Visual analogue scale
Less Same More
0 0 3
Numerical scale
Less Same More
3 0 0
Kappa
coefficient
0.10
3 0.47
4.13
122
ANIHONY E. R~ADINL
The relationship between pain indices and individual differences in terms of mood, anxiety and age are shown for both assessment occasions in Table 4. Age was negatively correlated with pain and anxiety indices, suggesting older patients were less anxious and experienced less pain. Mood was not significantly correlated with any of the measures, which may reflect the lack of range on the mood scale, as most women rated themselves towards the top of the scale. Trait anxiety was significantly correlated with both VAS (0.48) and numerical scale (0.42) ratings. State anxiety was significantly correlated with numerical ratings on day 1 (0.44) and with PPI (0.39) and VAS (0.49) on the second assessment occasion. DlSCUSSlON
The present study has examined the relationship between different indices of the verbal report of pain in terms of comparisons between rating scales and an analysis of the association between specific quality ratings and global ratings. It would be expected that measures with high similarity and purporting to tap the same aspect of the pain experience, in this case verbal report, would correlate highly. Thus, Woodforde and Merskey [16] compared four methods and found correlations ranged from -27 to +0.83 with the more similar procedures (VAS and verbal rating scale) correlating more highly. Similarly, Ohnhaus and Adler [17] reported a correlation of 0.81 between VAS and VRS ratings in a drug evaluation study. Variable correspondence between the scales emerged from the present study with a low correlation between VAS and PPI ratings on the first assessment occasion. The correlations between the numerical scale and the VAS were higher, possibly reflecting the similarity in format, as both involved ratings on horizontal, linear scales. On the second assessment occasion, the correlation between scales were significant (0.57-0.71), although lower than those reported elsewhere [16, 171. The associations between global ratings and ratings of specific pain descriptors were also examined. The pain adjectives reflected both specific sensory qualities and those concerned with the reactions to the pain. Overall ratings may be independent of the sensory experience, reflect the average of a range of sensory qualities or be selectively related to words reflecting a particular aspect of the pain sensations. The PPI was not related to quality ratings on day 1, suggesting that of the factors affecting these ratings, pain sensations may have had a relatively small influence. Alternatively, the VAS correlated more highly on both days with words reflecting the sensory qualities of the pain as compared with words indicating the reaction component. The high associations between the numerical scale and pain quality ratings may have been an artifact of the testing format, as the scales were similar, with the composition of the proforma permitting comparisons. From this analysis, it appears that the PPI may have been influenced by factors other than the sensory component of the pain. This interpretation is supported by previous research, as Melzack [5] reported low correlations between PPI ratings and adjective scores, suggesting this rating scale may reflect the patient’s psychological state at the time, emphasising the meaning attached to the pain sensations. In this case, the PPI ratings may have been influenced by attitudes towards the pain. The assessments were made in an emotional context, that of childbirth. It became apparent that women had widely varying reactions to the episiostomy. Some held strongly negative views concerning its perceived desirability and necessity, others
A comparison
of pain rating scales
123
124
ANTHONY E. READING,
felt positively towards it and a third group appeared ignorant as to its medical function. Change is of interest as many studies rely on changes in rating scale scores or verbal comparisons to demonstrate treatment efficacy. To expect global comparison and computed differences on rating scales to agree, assumes that each of these indices will be influenced to an identical degree by the many factors known to affect the pain experience. It is possible for example, that sensations may be reported via rating scales, even though global comparisons may describe the pain as reduced. The associations between computed rating scale differences and relational statements were generally less than satisfactory. Melzack [5] found the PPI scale correlated highly with percentage change ratings, although in the present study 7 women achieved higher ratings on the PPI in spite of declaring their pain diminished. In conclusion, this paper has considered the properties of commonly used scales in the assessment of pain in the medical setting. Insufficient attention has been directed towards establishing the psychometric adequacy of such scales. While no absolute generalisation can be made, as the performances of a scale may vary according to the context in which it is used and the sample characteristics, a methodology has been proposed whereby assessments can be subjected to more detailed analysis. By routinely establishing the correspondence between measures, greater confidence can be placed in the interpretation of results. If measures correspond poorly, it follows that reliance on a single measure may give rise to a misleading impression. The routine inclusion of quality assessments such as the McGill Pain Questionnaire [5] is to be recommended. REFERENCES 1. 2. 3. 4.
HUSKISSONE. C. Measurement of pain. Lancer ii, 1127 (1974). JOHNSON J. E. and RICE V. H. Sensory and distress components of pain. Nurs. Res. 23, 203 (1974). PECK R. E. A precise technique for the measurement of pain. Headache 6, 189 (1967). GRACELEY R. H., MCGRATH P. and DUBXER R. Ratio scales of sensory end affective verbal pain
descriptors. Pain 5,5 (1978). 5. MELZACK R. The McGill Pain Questionnaire: Major properties and scoring methods. Pain 1, 277 (1975). 6. READING A. E. and NEWTON J. R. A card sort method of pain assessment. J. Psychosom. Res. 22, 503 (1979). 7. BEECHER H. K. TheMeasuremenr of SubjectiveResponses. Oxford University Press, Oxford (1959). 8. MELZACK R. The Puzzle of Pain. Penguin, London (1973). 9. STERNBACH R. Clinical aspects of pain. In The Psychology of Pam, p. 241 (Edited by STERXBACH R. A.). Raven Press, London (1978). 10. MELZACK R. and CASEY K. L. Sensory, multidimensional and central control determinants of pain. In TheSkin Senses, p. 423 (Edited by KERSHALD. R.). Thomas, Springfield (1968). 11. GRACELEY R., MCGRATH P. and DUBNER R. Validity and sensitivity of ratio scales of sensory and
affective verbal pain descriptors. Manipulation of effect by diazepan. Pain 5. 19 (1978). 12. SCOTT J. and HUSKISSON E. C. Graphic representation of pain. Pain 2, 175 (1976). 13. FREDERICKSONL. W. Methodology in the measurement of pain. Behav. Ther. 9,486 (1978). 14. READING A. E. and Cox D. N. The Measurement of Pain in Research in Psychology and Medicine, Vol. I, p. 20 (Edited by OBORNE D. J., GRUNEBERC M. and EISER D. R.). Academic Press, London (1979). 15. SPIELB~RGER C. D., GORSUCH R. L. and L~SHENE R. E. State-Trait Anxiety Inventory Manual. Consulting Psychologists Press Inc., Palo Alto (1970). 16. WOODFORD J. M. and MERSKEY H. Some relationships between subjective measures of pain. J. Psychosom. Res. 16, 173 (1972). 17. OHNHAUS E. E. and ADLER R. Methodological problems in the measurement of pain: a comparison between the verbal rating scale and the visual analogue scale. Pain 1, 379 (1975).
A COMPARISON
OF PAIN RATING
ANTHONY (Received
E.
SCALES
READING
11 December
1979)
Abstract-In
the course of studying episiotomy pain in a small group of women (n = 26), a number of commonly used rating scales were compared. The results showed wide variation in the distribution of ratings between scales. Variation also emerged with respect to the degree of concordance between rating scale differences over time and subjective comparisons. The implications of these results are considered in terms of: (a) the way in which reliance on single rating scales may give rise to a misleading impression; and (b) the need to assess the various components of pain. Routine inclusion of multidimensional assessment methods is recommended. IN SPITE of advances in pain understanding and management, the assessment of the verbal report of clinical pain remains a difficult yet important task. Assessment may assist in diagnosis, thereby ensuring the appropriate treatment programme is selected. Similarly, evaluations of new treatment methods depend upon the availability of measures that reliably reflect fluctuations in the pain experience. A number of indices have been used: including rating scales [l], combinations of rating scales [2], cross modality matching [3, 41, questionnaires [5] and a card sort method [6]. Rating scales which focus on intensity only have been criticised owing to their failure to reflect adequately the multidimensional nature of pain [5]. Pain is a complex experience influenced by many factors in addition to the sensory input such as culture, emotions, psychological processes and reinforcement contingencies [7-91. There is evidence for two main dimensions of pain; sensory-discriminative and evaluative-emotional [lo, 111. The latter can be thought of as a flexible lens magnifying or reducing the amount of sensation that is felt. However, in spite of their limitations, self report scales-verbal, visual or numerical-have been the most commonly reported index [ 12, 131. It is apparent that more information is needed as to the adequacy and comparability of pain ratings scales, given their widespread usage. For example, where labels or anchor points are included, difficulties may result from the assumption that various complex definitions constitute a properly ordered scale. In fact, it is possible that patients may not be able to discriminate reliably between the points on the scale, and for some the points may not even be on the same dimension [ 141. The words supplied may also influence the distribution of responses, with anchor points determining where a non-uniform or uniform distribution of scores is obtained [12]. In the course of studying patient reactions to episiotomy a number of pain assessment scales were administered, permitting comparisons between different methods. Ratings were also made of specific pain adjectives reflecting both the sensory and evaluative components of pain. Three questions were addressed: (a) the correspondence between pain ratings on unidimensional rating scales; (b) the degree to which global ratings reflect specific aspects of the pain experience; and (c) the degree to which rating scales reliably reflect change over time. Senior Clinical Psychologist/Lecturer at the Department of Psychological Hospital Medical School, Denmark Hill, London SE5 8RX, U.K. 119
Medicine,
King’s
College
120
ANTHONY E. READING METHOD
A consecutive series of 26 women undergoing mediolateral episiotomy during childbirth were studied (mean age 24.6 yr; S.D. 5.3). All were fluent in English and had given birth to normal babies. None refused to take part in the study and all were told the assessments and interviews were for research purposes. The women were interviewed on successive days following delivery and at least 6 hr after receiving pain killing medication where this had been requested. On both occasions the episiotomy pain was assessed on a number of rating scales. These were: (a) the Present Pain Intensity (PPI) verbal rating scale [S], consisting of the adjectives “mild-discomforting-distressing-horrible-excruciating”: (b) a visual analogue rating scales (VAS) in the form of a 10 cm horizontal line with anchor points at both ends consisting of “no pain at all” and “worst pain imaginable”; (c) a IO-point horizontal numerical scale with verbal anchor points consisting of “none-mild-moderately distressing-very distressingunbearable”. In addition the quality of the pain was investigated by asking women to rate on 7 point scales a number of specific pain adjectives which were drawn from the McGill Pain Questionnaire (MPQ, [5]). Anxiety was assessed on the Spielberger State Trait Anxiety Inventory [15] and depression on IO-point ladder scales with 0 reflecting total depression and the top (10) completely happy.
RESULTS The mean scores on the three rating scales are shown in Table 1, along with Pearson product moment correlations between them. The means indicate a discrepancy between the PPI and the other two scales, with patients tending to score higher on the PPI. On the first day correlations were low, with only the association between the numerical scale and the VAS reaching significance (r = 0.46). The following day less variation in pain scores was evident, with correlations higher and all significant.
TABLE 1.-CORRELATIONS BETWEENPAIN RATINGSC-ZLESON EACH TESTINGOCCASION
Present
pain intensity
Visual analogue Numerical
scale
scale
day day day day day day
Mean
S.D.
3.3 4.3 27.2 19.5 4.0 2.9
(1.5) (1.1) (19.5) (15.5) (2.0) (1.7)
1 2 1 2 1 2
Visual analogue 0.29 (0.711_)
scale
Numerical
scale
0.26 (0.57*) 0.46t
(0.62-t)
Day two correlations in parentheses. *P< 0.05; fP< 0.01.
Correlations were also computed between global ratings and individual quality ratings on the adjective checklists and are presented, with mean ratings for each adjective for each day, in Table 2. It can be seen that the following words were used to describe the postepisiotomy pain on both assessment occasions: “throbbing, cramping, pulling, stinging, aching, tiring and annoying”. Pearson product moment correlations were higher on the second day postpartum. On day 1 no significant correlations emerged between the PPI and individual pain descriptors. Two words correlated significantly with the VAS score (pulling: r = 0.37; and throbbing: r = 0.52). On the second day, the VAS was significantly correlated with 5 words reflecting the sensory qualities of the pain (throbbing, shooting, stabbing, cutting and burning). In contrast, the majority of adjectives correlated significantly with the numerical rating scale scores.
A comparison
121
of pain rating scales
TABLE~.--MEANRATINGS~NADJECT~VESANDC~RRELAT~~NSW~THGLOBALRAT~NGSCALESFORBOTHTEST~NG OCCASIONS
Rating scale Mean score Pain adjective
I
day
Throbbing Shooting Stabbing Cutting Cramping Pulling Burning Stinging Aching Tiring Sickening Terrifying Punishing Annoying Unbearable *P< 0.05; fP<
1.7 1.2 1.3 1.4 1.4 1.6
1.o 1.9 3.0 1.4 1.3 0.3 0.8 2.7 1.2
Present
pain intensity
Numerical
Visual analogue
day 2
day 1
day 2
day 1
1.5 0.4 0.7 0.7 1.3 2.0 0.6 1.6 2.0 1.2 0.5 0.7 0.1 1.5 0.2
0.00 0.25 0.21 0.17 0.22 -0.02 0.12 0.22 0.16 0.15 0.12 0.29 0.06 0.06 0.21
0.51* 0.23 0.19 0.39 0.43 0.41 0.13 0.16 0.31 0.11 0.20 0.10 -0.23 0.47” 0.15
0.52t 0.06 -0.06 0.04 0.09 0.37* -0.07 0.07 0.13 0.02 -0.05 0.11 -0.01 0.16 0.06
I
day 2
day
0.70-f 0.78-f
0.63-t
0.50* 0.62t 0.33 0.42 0.55t 0.26 0.41 0.13 0.21 0.72t -0.14 0.15 0.27
0.62t
0.61t 0.61t 0.46t 0.72t 0.52t 0.49t 0.55t 0.51t 0.69t 0.62t 0.43* 0.43* 0.70t
day 2 0.42 0.39 0.54* 0.69t 0.34 0.71t 0.72T 0.63t 0.83t 0.40 0.68$ 0.25 0.46* 0.61t 0.52*
0.01.
In order to assess the sensitivity to change of each of the scales, the differences between ratings on day 1 and day 2 were computed. These were compared with responses to the question “how does the pain you are now experiencing compare with the one at the time of the assessment yesterday?” Of the sample of 26 women, only 19 were experiencing sufficient pain at the time of the second interview to complete the scales. Answers to this question were translated into greater, same or less and kappa coefficients of agreement were computed between these subjective comparisons and the computed rating score differences. The results are shown in Table 3 for each of the pain rating scales. Ideally, with high concordance, the majority of patients would fall in the top-left to bottom-right diagonal. As shown in Table 3, there was a wide distribution with some women reporting less pain and yet achieving higher scores on the rating scales. The highest kappa coefficient was found for the VAS (0.47), with 11 of the sample lying in the diagonal. Lower levels of agreement were found for the numerical and PPI scales. TABLE ~.--CORRESPONDENCEBETWEENGLOBALCOMPARlSONSANDCOMPUTEDRATlNGSCALEDlFFERENCES
Global comparisons Rating scale
Less
Same
More
Present pain intensity
Less Same More
0 0
Visual analogue scale
Less Same More
0 0 3
Numerical scale
Less Same More
3 0 0
Kappa
coefficient
0.10
3 0.47
4.13
122
ANIHONY E. R~ADINL
The relationship between pain indices and individual differences in terms of mood, anxiety and age are shown for both assessment occasions in Table 4. Age was negatively correlated with pain and anxiety indices, suggesting older patients were less anxious and experienced less pain. Mood was not significantly correlated with any of the measures, which may reflect the lack of range on the mood scale, as most women rated themselves towards the top of the scale. Trait anxiety was significantly correlated with both VAS (0.48) and numerical scale (0.42) ratings. State anxiety was significantly correlated with numerical ratings on day 1 (0.44) and with PPI (0.39) and VAS (0.49) on the second assessment occasion. DlSCUSSlON
The present study has examined the relationship between different indices of the verbal report of pain in terms of comparisons between rating scales and an analysis of the association between specific quality ratings and global ratings. It would be expected that measures with high similarity and purporting to tap the same aspect of the pain experience, in this case verbal report, would correlate highly. Thus, Woodforde and Merskey [16] compared four methods and found correlations ranged from -27 to +0.83 with the more similar procedures (VAS and verbal rating scale) correlating more highly. Similarly, Ohnhaus and Adler [17] reported a correlation of 0.81 between VAS and VRS ratings in a drug evaluation study. Variable correspondence between the scales emerged from the present study with a low correlation between VAS and PPI ratings on the first assessment occasion. The correlations between the numerical scale and the VAS were higher, possibly reflecting the similarity in format, as both involved ratings on horizontal, linear scales. On the second assessment occasion, the correlation between scales were significant (0.57-0.71), although lower than those reported elsewhere [16, 171. The associations between global ratings and ratings of specific pain descriptors were also examined. The pain adjectives reflected both specific sensory qualities and those concerned with the reactions to the pain. Overall ratings may be independent of the sensory experience, reflect the average of a range of sensory qualities or be selectively related to words reflecting a particular aspect of the pain sensations. The PPI was not related to quality ratings on day 1, suggesting that of the factors affecting these ratings, pain sensations may have had a relatively small influence. Alternatively, the VAS correlated more highly on both days with words reflecting the sensory qualities of the pain as compared with words indicating the reaction component. The high associations between the numerical scale and pain quality ratings may have been an artifact of the testing format, as the scales were similar, with the composition of the proforma permitting comparisons. From this analysis, it appears that the PPI may have been influenced by factors other than the sensory component of the pain. This interpretation is supported by previous research, as Melzack [5] reported low correlations between PPI ratings and adjective scores, suggesting this rating scale may reflect the patient’s psychological state at the time, emphasising the meaning attached to the pain sensations. In this case, the PPI ratings may have been influenced by attitudes towards the pain. The assessments were made in an emotional context, that of childbirth. It became apparent that women had widely varying reactions to the episiostomy. Some held strongly negative views concerning its perceived desirability and necessity, others
A comparison
of pain rating scales
123
124
ANTHONY E. READING,
felt positively towards it and a third group appeared ignorant as to its medical function. Change is of interest as many studies rely on changes in rating scale scores or verbal comparisons to demonstrate treatment efficacy. To expect global comparison and computed differences on rating scales to agree, assumes that each of these indices will be influenced to an identical degree by the many factors known to affect the pain experience. It is possible for example, that sensations may be reported via rating scales, even though global comparisons may describe the pain as reduced. The associations between computed rating scale differences and relational statements were generally less than satisfactory. Melzack [5] found the PPI scale correlated highly with percentage change ratings, although in the present study 7 women achieved higher ratings on the PPI in spite of declaring their pain diminished. In conclusion, this paper has considered the properties of commonly used scales in the assessment of pain in the medical setting. Insufficient attention has been directed towards establishing the psychometric adequacy of such scales. While no absolute generalisation can be made, as the performances of a scale may vary according to the context in which it is used and the sample characteristics, a methodology has been proposed whereby assessments can be subjected to more detailed analysis. By routinely establishing the correspondence between measures, greater confidence can be placed in the interpretation of results. If measures correspond poorly, it follows that reliance on a single measure may give rise to a misleading impression. The routine inclusion of quality assessments such as the McGill Pain Questionnaire [5] is to be recommended. REFERENCES 1. 2. 3. 4.
HUSKISSONE. C. Measurement of pain. Lancer ii, 1127 (1974). JOHNSON J. E. and RICE V. H. Sensory and distress components of pain. Nurs. Res. 23, 203 (1974). PECK R. E. A precise technique for the measurement of pain. Headache 6, 189 (1967). GRACELEY R. H., MCGRATH P. and DUBXER R. Ratio scales of sensory end affective verbal pain
descriptors. Pain 5,5 (1978). 5. MELZACK R. The McGill Pain Questionnaire: Major properties and scoring methods. Pain 1, 277 (1975). 6. READING A. E. and NEWTON J. R. A card sort method of pain assessment. J. Psychosom. Res. 22, 503 (1979). 7. BEECHER H. K. TheMeasuremenr of SubjectiveResponses. Oxford University Press, Oxford (1959). 8. MELZACK R. The Puzzle of Pain. Penguin, London (1973). 9. STERNBACH R. Clinical aspects of pain. In The Psychology of Pam, p. 241 (Edited by STERXBACH R. A.). Raven Press, London (1978). 10. MELZACK R. and CASEY K. L. Sensory, multidimensional and central control determinants of pain. In TheSkin Senses, p. 423 (Edited by KERSHALD. R.). Thomas, Springfield (1968). 11. GRACELEY R., MCGRATH P. and DUBNER R. Validity and sensitivity of ratio scales of sensory and
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