- Email: [email protected]
A parsimonious set of verbal descriptors of pain sensation derived from the McGill Pain Questionnaire
Pain, 1
(
3
International Associationfor the Study of Pain. All rights reserved0304-3959/96/$15.00
PAIN 2992
A parsimonious set of verbal descriptors of pain sensation derived from the McGill Pain Questionnaire Ephrem Fernandez* and Stuart Towery D
P
S
M
U
D
T
7
(
(Received8 June 1995;revisionreceived22 August 1995;accepted20 September1995)
s In view of some recent disagreementsabout the vocabulary of pain as suggestedin the McGill Pain Questionnaire(MPQ), the present study re-examinedall MPQ pain descriptorswith regard to their appropriateness as descriptorsof pain sensation.A sampleof 70 undergraduatestudents (whosefirst languagewas English)assigned descriptorsto individualsensorysubcategoriesand then rated them in terms of impliedintensityof pain. Data were evaluated using three criteria related to the absolute frequency, relative frequency, and unimodality of word assignmentsto each subcategory.Results revealedthat about 400/0of the supposed MPQ sensorydescriptorscould not be classifiedwithinany of the sensorysubcategoriesbecauseof incomprehension,underuse,or ambiguityof usage. The majority of the words, however,were classifiedin the same subcategoriesand given similarintensityratings as in the MPQ. Thesewordsconstitutea parsimonioussubsetof MPQ descriptorsof pain sensation.Suchwords promise more diagnosticspecificityin the assessmentof pain. Further research could serveto replicatethese findingsas part of the ongoing refinementof the MPQ. Pain descriptors;Sensation;Classification;MPQ; Decisionrule
and
I
categoriesas wellas an additional category.The sensorycategoryencompasses10subcategories: p
m
Becausepain is a subjective,private experience,languageoffers a usefulmethod of labelingthis phenomenon; apart from its value in mental representation, languagealso servesas a tool in the communicationof pain to others. Words may be used to convey multidimensionalproperties of pain, such as intensity, sensation,and affectivereaction,whichare of particular diagnosticvalue to clinicians. The first systematic attempt to incorporate verbal descriptors in pain assessment was the McGill Pain Questionnaire or MPQ (Melzack 1975),currently the most widelyused instrumentin pain research and practice. The MPQ is a self-reportinstrument that presents 78 pain dewriptors distributed across 20 subcategories (with an additional 6 words in the Present Pain Index); theseare further organizedinto thrm broad sensory, *C 7
7
e-mail:[email protected]. sun.edu.
‘
p
T S 0
S
c
and For example,the word contained within the subcategory whereas the word falls within the subcatego~. The implicationis that each word reflects a particular sensoryproperty of pain. The affectivecategory containswords such as and which are supposed to reflect negativeemotion and its autonomic properties. Finally, the evaluativecategory containswordsrangingfrom to e which reflect the overall intensity of pain. In addition, each word from each category has a rank value indicativeof the relativeintensityof pain implied. Psychometrically,the MPQ meets several important criteria. Adequate test-retest reliability has been demonstratedfor someof the word subcategories(Love et al. 1989)and internal consistencyhas been shown in the case of cancer patients (Graham et al. 1980).MPQ ratingshave also been found to be sensitiveto standardized stimuli (Klepac et al. 1981), and capable of discriminatingbetweenacute and chronic pain (Teman b
3
32
and Dar 1986),betweenfunctionaland organic aspects of pain (Leavittand Garron 1980)and betweenvarious pain syndromes(Metzacket al. 1986).Concurrentvalidity has been observed with visual analogue ratings of pain (Walsh and Leber 1983) as well as medication dosageand recoverytime (Van Buren and Kleinknecht 1979). The successof the MPQ is further establishedby its translation or adaptation for use in more than a dozen languages. These include many of the European languages and others ranging from Arabic to Japanese. Clearly, in spite of the linguisticrelativity, there is a common need for a.vocabulary of pain. There are indications, however, that the MPQ pain vocabulary can be refined. For instance, the factor structure of the MPQ has been unstable across studies. As reviewedby Femandez and Turk (1992),the pool of MPQ pain descriptorsgenerallyrevealsa sensoryfactor, and lessoften,an affectivefactor, but the evaluativefactor has been difficultto uncover.In severalfactor analytic investigations,two or more of the factors also have beenconfoundedwith on? another. This probablyarises from the underlyingproblemswith the selectionand organizationof the verbaldescriptorsof pain in the MPQ. Focusingon the sensorycategoryalone, many inconsistenciesmay be noted regarding the classificationof words into the 10 MPQ sensory subcategories (Fernandez and Boyle 1994;Towery and Femandez 1994). Employingcluster analysis,for instance, Reading et al. (1982)found that the word was a descriptorwhereasit had been classifiedas in the MPQ. The word was a descriptorof b in pain rather than as indicatedby the MPQ, and the word was indicative of rather than d as suggestedby the MPQ. Similarly, Clark et al. (1993)employedhierarchicalclusteringto come up with an expanded list of pain descriptors organized along a new set of dimensions.Hase (1992) recentlyturned to rational approaches for reclassifying the existingMPQ words into subcategoriesas well as changingthe labels given to certain subcategories. These recent departures are suggestiveof difficulties in the classificationof MPQ descriptors. First of all, several words have multiple meanings. The very first word on the list,f has been classifiedas since it impliesa periodicityof occurrence.On the other hand, it may also be classified within the b subcategoryby virtueof its referenceto visual phenomena.Other words suchas implyboth sensoryand affectivequalitiesand hencemay appear in different subcategories or even different categories altogether. This ambiguity of meanings also has been observedby Torgersonand BenDebba(1983)in their research on multidimensionalscalingof pain descriptors. It also may be noted that many of the words in the sensorycategory of the MPQ are metaphors of the ac-
tions producinginjury or pain. Thus, there is no physical sensationthat is intrinsicallyof a quality, or for that matter, a quality; and are merelyactionsthat can potentiallylead to pain. The word then would have little if any place in the vocabularyof a pain patient who had neverbeen stabbed before. Yet, because pain is often so difficult to describe,patients may resort to metaphors in an effort to communicatetheir experience. Additionally, some words in the MPQ are incomprehensible.In our clinical experience,the word often evokesquestionsfrom patients about its meaning.Similarly, a word that patients seek clarificationon. Yet, other words in the MPQ may be comprehensiblebut are rarelyendorsedbecausethey are only marginallyrelevantto the experienceof pain. In a meta-analysisof 51 studiesusingthe MPQ, Wilkieet al. (1990)found that of the 78 MPQ words that describe pain quality,only 19words were selectedby more than 20%of subjects.Many of the translations and adaptations of the MPQ also arrive at a substantial reduction in the numberof descriptorsas compared to the original Englishversion,thus raisingthe possibilitythat the (universal)vocabularyof pain is smallerthan that suggested in the MPQ. An ancillaryproblemconcernsthe labelsgivento subcategoriesof pain descriptors.Someof theselabelssuch as are not clearly differentiated from other subcategory labels such as Others such as may be misnomers; in the MPQ, pitted against and contains words like and rather than or f Therefore, the term may be more appropriatethan b Finally,it is contendedthat the subcategoriesof and are really dimensionsof pain, as in the multi-axialIASP Pain Taxonomy (Merskey 1986), rather than classes of pain descriptors.These dimensionscan be used in conjunction with any class of sensorypain descriptors;thus, it wouldmake senseto speakof a pain with a thermal property of that also is spatiallydefinablein terms of an anatomical site on the body and tempolally definablein terms of its continuous or episodicfeature as the case may be. In view of the above issues, more careful consideration needs to be given to the selectionof meaningfid pain descriptors and the labeling of associated subcategories.Furthermore, the intensityrankings of these descriptorsas suggestedin the MPQ are in need of replication. In attemptingthesedual tasks, the present study focuses exclusivelyon the sensory descriptors of the MPQ. This category accounts for the bulk of MPQ descriptorsand has beenwidelyvalidatedin factor analytic investigations.Moreover, it is the sensation that definesthe intrinsicphysicalqualityof the pain whileaffectis primarilya reactivecomponentof pain. Through
33
the extraction of unambiguousdescriptorsof pain sensation and confirmation of the intensity values, languagecan be used more accuratelyin the qualitativeand quantitativeassessmentof pain. This process is undertaken in viewof Melzack’s(1975)invitation for further research and refinementof the MPQ.
1 D
Subjects A total of 70 students from an undergraduateclass in health psychologyat Southern Methodist Universityparticipated in the study. Subjectswere betweenthe ages of 17and 27 and reportedlyin good physicalhealth. P
Participationin the studywas a course requirementfor whichsubjects receivedthree points towards their course grade. Rules of informedconsent were adhered to and subjectswere free to withdraw without ~nalty. AHsubjectswere presentedwith a list of 84 pain descriptorsfrom the McGill Pain Questionnairewhich were to be classifiedinto sensory, affective,and evaluativecategoriesof the MPQ. The individual subcategory labels were not defined for subjects but were supplemented with the most representative example drawn from the descriptor list (on the basis of pilot data). Subjects were free to reclassifythe exampleitself, to classifywords into any subcategories, to add new words to the list, or to leave any word unclassified altogether. Apart from the c(assitication, subjects also provided numericalratings of intensity implied by each descriptor. This was donein referenceto a rating scalerangingfromO(no pain)to 10(maximumpain). D
P
Cutting Lacerating Comtrietive
66 42
a
Giventhe exclusivefocus on descriptorsof pain sensation,tbe frequencywith whicheach word appeared in each sensorysubcategory wastallied.A three-stepdecisionrule wasthen appliedto the frequency data to determine which pain descriptors related to each subcategory:(i) the absolute frequencywith whicha word was assigned to a subcategoryhad to exceedthat expectedunder a binomialprobabilityof 0.01;based on this, the minimumfrequencyrequiredwas 10; (ii) the relativefrequencythat a word was assignedto a subcategory (over atl alternative subcategoriesused) had to exceed 1/2;(iii) when a word met criteria for more than one subcategory,it was granted membershipin the subcategoryit wasmost frequentlyassignedto (the mode);however,when a word was bimodallydistributed across two subcategoriesit was considered ambiguousand therefore excluded. The combinationof the three criteria above was applied order to reach a decision regarding which words tit best into which s categories. In addition, means were computed for intensity ratings givenfor each word withineach subcategoryit had heen assignedto.
B
30
Using this conservativedecision rule, it was found that 32out of a total of 84 MPQ descriptorsmet criteria for classificationin the 10sensorysubcategories(Table I). This further means that 23 of the 55 (supposed)sensory descriptorsin the MPQ failed to meet criteria for inclusionin any singlesensory subcategory. Fig. 1 illustrates the 10 most frequently assigned words for each subcategory. However, many of these wordsattained frequenciesof lessthan 10,and so based on the binomialformula (criterion 1)theseobservedfre-
quencieswere not significantlydifferent from chance. For example,in the subcategory,the words p and attained frequenciesof 6, 7, and 8, respectively,and thus wereexcluded.Similarly, in the subcategory,three words and pinching)wereidentifiedfor exclusion,and for the subcategoriesof and at
34
Temporal ,
b
~ b J .
q &
I
l s
p
t 8
10
?-0
30
40
SO
60
0
;Q
10
xl
30
a
50
60
70
W
F
Punctate Pressure c h s , p ,
1~I I
s !
v L
a
s s
o
10
?-0
30
40
50
60
70
0
F
10
24
30
40
50
60
;O
i
C
60
70
F
C r
f
l
S
“
U 0
10
24
30
40
50
60
F
B .
S
I
a
b
s r m L , , .
Fig. 1. The frequencyof assignmentof words across subcategories.
l
35
leasthalf of the words warranted exclusionon the basis of this criterion. Having met the criterion of absolute frequency, membership in a subcategory also required that a descriptorhad to be assignedto that subcategoryin at least 5 of instancesas compared to its assignmentto all alternative subcategoriesused (criterion 2). For example,the word p attained an absolutefrequency of greater than 10in both the subcategoriesof p and i but had a relativefrequency of 0.33 in the latter subcategory and 0.51 in the former subcategory;in viewof this it was deemedmore appropriate as a descriptorof p Table I summarizesthe relative frequencies of all words that met criteria 1 and 2. The third and final criterion that all words had to satisfy for membership in a subcategory was that of unimodality.In other words, descriptors that attained suftlcientlyhigh absoluteand relativefrequencies,could not be bimodallydistributedacrosssubcategoriesif they wereto be granted membershipin a singlesubcategory. For example, the word l met both criteria 1 and 2 for i and p subcategories(Fig. 2). Therefore,it was deemedambiguous and excluded.Words such as andjlashing (Fig. 2) were also bimodalin their distributionand consequentlydeniedmembershipin any singlesubcategory. The final list of descriptorsthat met criteria for indi-
vidual subcategoriesof pain sensation are presented in Table I. On the average, three words emerged in each subcategoryas compared to the average of four words within subcategoriesof the MPQ. The actual classification of thesewords departed minimallyfrom that in the MPQ. For example, the descriptors within the subcategoriesof and wereidenticalto those in MPQ subclasses7 (thermal) and 19 (miscellaneous). For the and subcategories,notwithstandingthe few words excluded,all words retained matched those in the MPQ subcategories.The subcategoriesof s and contained some of the original words from corresponding MPQ subcategoriesas wellas new words which in all casescame from the MPQ miscellaneousgroups. The subcategorywasthe onlyonewhichcontainedan altogether new set of words;these words also had been previously designatedas miscellaneousin the MPQ. Finally,mean intensityratingsof each classifiedword are listed in Table I. As shown, individual descriptors withineach subcategorydiffer in terms of their implied intensityand could be rank-ordered accordingly.More importantly, the intensity ratings of this final set of wordsweresignificantlycorrelatedwith those originally reported by Melzackand Torgerson (1971) = 0.91, P <
0
Lancinating
Tearing
Hotness
O
4
4
Flashing
Numb Others
s
s
Brightness 35%
Fig. 2. ‘Lancinating’,‘Tearing’,‘Numb’,and ‘Flashing’as classifiedacross subcategories.
36
D
Proceedingfrom the research of Melzackand Torgerson (1971) and Melzack (1975), the present study investigatedthe classificationand intensity ratings of pain descriptorswithin a sample of universitystudents conversantin the Englishlanguage.However,the samplesizeof subjectsperformingthe classificationtask was considerablylarger in this study. The classificationtask itselfwas more stringentin that subjectsactuallyhad to assignwords to subcategoriesrather than merelyagree/ disagreewith the preexistingclassification.In rating the intensity of pain suggestedby each word, an interval scalewas used instead of a categoricalscale. Despite the above methodological departures, the findingsof this studyare remarkablyconsistentwith the originalorganizationof MPQ descriptorsof pain sensation, but they do providegroundsfor streamliningthese descriptors. Specifically,about 60Y0of the descriptors appearing in sensory and sensory-miscellaneous categoriesof the MPQ were retained, leaving23 words to be excludedbecauseof failure to meet the polythetic criteria of this study. First of all, somewords were not assignedfrequently enough to any subcategoryas to permit a rejection of the null hypothesis of random assignment.The word was among the very lowest in frequency, and therefore an underused word. This may be attributable to the failureof many subjectsto comprehendthe word or to grasp its relevanceto the communication of pain. Likewise,we have observed that pain patients have notable difficultyin understandingsuch words or relating them to pain. Such words are best excluded. Other wordswarranted exclusionbecauseof their low relative frequencies of assignment to any single subcategory.For example,the word appeared more than 10 times in the subcategory,but this accounted for less than 50% of the instancesin which it was assigned across all subcategories.By implication, t not reliably linked to temporal features of pain (or for that matter any other sensory property of pain); therefore, it was excludedfrom the final list. Thosewords that attained a suftlcientlyhigh absolute frequencyand relativefrequencybut were more or less equally distributed across more than one subcategory werenot retained.This is consistentwith Torgersonand BenDebba’s findings (1983) that some MPQ pain descriptorsare not definitiveof pain quality. Common in usage though they may be, these descriptors lack specificityof meaningand thus confound the interpretation of pain. Therefore,wordssuch as numbandflashing were excludedaltogether.The word was found to connote either coldness or dullness, while the word j wasfound to refer to either b or aspects of pain. Because of the high degree of ambiguitywhich detracts from the discriminantutility
of such words, they were not includedin the new set of descriptors. Conversely,the 32 words which met all criteria for retention were used frequently and unambiguouslyin the communicationof pain. These words represent a subsetof the originalMPQ descriptors,but their precise placementin individualsubcategoriescloselyresembles that laid out in the MPQ. Nearly all the new words in the subcategoriesactuallycame from the miscellaneous class of the MPQ suggestingthat several descriptors previously viewed as ambiguous in fact could be classified. Apart from the similarity in classification, the retained descriptors also correlated highly with the MPQ in termsof intensityratings.This representsa replicationof the seminalfindingby Melzack and Torgerson (1971)that verbaldescriptorscan be used reliablyto differentiatenot only among the qualitative aspects of pain but also to discern quantitativevariations in pain. It also adds to the levelof confidencein the diagnostic specificityof the new set of descriptors. Consequently, clinicianscouldmakeinferencesabout the sensationand underlyingpathology of pain as well as its magnitude. In short, this study suggestsa new subsetof pain sensation descriptors that excludes several words on the grounds of infrequencyand ambiguityof usage, yet retains most of the words from the original list in the MPQ, preservesmuch the sameorganizationof theseretained words across subcategories,manages to classify many words that were once left unclassified,and also replicates pain intensity ratings implied by each word retained. The end result is a more parsimonious collectionof descriptorsof pain sensation.In achieving this end, the present study has followed the direction started by the MPQ and the vision expressed by its authors for the continuedrefinementof the languageof pain. Future researchmight address the replicabilityof the presentfindingsin the population of pain patients who are the most likely users of pain descriptors. Crosslinguistic studies may be undertaken to assess the generalizabilityof thesefindings.Finally,sincethe present studywas confinedto descriptorsof pain sensation, it is necessaryto expandthe scopeof inquiryto affective descriptorsof pain as well. R Clark,C.W., Fletcher,J.D., Janal, M.N. and Carroll, J.D., Hierarchicalclusteringof 270descriptorsinto a pain, suffering,and pleasure space;their relationshipto the McGill Pain Questionnaire.In: B. Brommand J. Desmedt(Eds.),Pain and the Brain:From Nociception to Cortical Activity, Raven Press, New York, 1993,pp. 319-330. Femandez, E. and Boyle,G., A reconsiderationof the languageof pain with reference to the McGill Pain Questionnaire, Paper
37 presentedat the Twenty-ThirdInternational Congressof Applied Psychology,Madrid, 1994. Femandez, E. and Turk, D.C., Sensoryand affectivecomponentsof pain: separationand synthesis,Psychol.Bull., 112(1992)205-217. Graham, C., Bond, S.S., Gerkovich,M.M. and Cook, M.R., Use of the McGill Pain Questionnairein the assessmentof cancer pain: replicabilityand consistency,Pain, 8 (1980)377-387. Hase, H.D., McGill Pain Questionnaire: Revised format. In: L. VandeCreek,S. Knapp and T.L. Jackson (Eds.), Innovationsin ClinicalPractice:A SourceBook,Vol. 11,ProfessionalResource Press, Sarasota, FL, 1992,pp. 285-291. Klepac, R.K., Dowling,J. and Hauge, G., Sensitivityof the McGill Pain Questionnaireto intensity and quality of laboratory pain, Pain, 10(1981)199-207. Leavitt, F. and Garron, D.C., Validityof a back pain classification scale for detectingpsychologicaldisturbanceas measured by the MMPI, J. Clin. PsychoI.,36 (1980)186–189. Love, A., Leboeuf,D.C. and Crisp, T.C., Chiropractic chronic low back pain sufferersand self-reportassessmentmethods,Part 1,A reliabilitystudy of the Visual AnalogueScale, the pain drawing and the McGill Pain Questionnaire,J. Manip. Physiol.Ther., 12 (1989)21-25. Melzack,R., The McGill Pain Questionnaire:Major properties and scoringmethods, Pain, 1 (1975)277-299. Melzack, R., Terrcnce, C., From-n, G. and Amsel, R., Trigeminal neuralgiaand atypical facial pain: usc the McGill Pain Questionnaire for discrimination and diagnosis, Pain, 36 (1986) 225-229.
Melzack,R. and Torgerson,W.S., On the languageof pain, Anesthesiology,34 (1971)50-59. Merskey,H., Classificationof chronic pain: descriptionsof chronic pain syndromesand definitionsof pain terms, Pain, Suppl.3 (1986) S21-S225. Reading,A.E., Everitt, B.S. and Sledmore,C.M., The McGill Pain Questionnaire: a replication of its construction, Br. J. Clin. PsychoI.,21 (1982)339-349. Teman, B.H. and Dar, R., Physicianratings of pain descriptors:potential diagnosticutility, Pain, 26 (1986)45-51. Torgerson,W.S. and BerrDebba,M., The structure of pain descriptors. In: R. Melzack (Ed.), Pain Measurementand Assessment, Raven Press, New York, 1983,pp. 49–54. Towery, S. and Femandez, E., Describing pain sensations: MPQ wordsbased on a new decisionrule, Paper presentedat the Thirteenth Annual ScientificMeeting of the American Pain Society, Miami, 1994. Van Buren,J. and Kleinknecht,R.A., An evaluation of the McGill Pain Questionnaire for use in dental pain assessment, Pain, 6 (1979)23-33. Walsh, T.D. and Leber, B., Measurement of chronic pain: Visual analog scalesand McGill Melzackpain questionnairecompared. In: J.J. Bonicaet al. (Eds.),Advancesin Pain Researchand TheraPY, Vol. 5, Raven Press, New York, 1983,pp. 897-899. Wilkie,D.J., Savedra,M.C., Holzemer,W.L., Tesler, M.D. and Paul, S.M., Use of the McGill Pain Q m pain: a meta-analysis,Nurs. Res., 39 (1990)36-41.
(
3
International Associationfor the Study of Pain. All rights reserved0304-3959/96/$15.00
PAIN 2992
A parsimonious set of verbal descriptors of pain sensation derived from the McGill Pain Questionnaire Ephrem Fernandez* and Stuart Towery D
P
S
M
U
D
T
7
(
(Received8 June 1995;revisionreceived22 August 1995;accepted20 September1995)
s In view of some recent disagreementsabout the vocabulary of pain as suggestedin the McGill Pain Questionnaire(MPQ), the present study re-examinedall MPQ pain descriptorswith regard to their appropriateness as descriptorsof pain sensation.A sampleof 70 undergraduatestudents (whosefirst languagewas English)assigned descriptorsto individualsensorysubcategoriesand then rated them in terms of impliedintensityof pain. Data were evaluated using three criteria related to the absolute frequency, relative frequency, and unimodality of word assignmentsto each subcategory.Results revealedthat about 400/0of the supposed MPQ sensorydescriptorscould not be classifiedwithinany of the sensorysubcategoriesbecauseof incomprehension,underuse,or ambiguityof usage. The majority of the words, however,were classifiedin the same subcategoriesand given similarintensityratings as in the MPQ. Thesewordsconstitutea parsimonioussubsetof MPQ descriptorsof pain sensation.Suchwords promise more diagnosticspecificityin the assessmentof pain. Further research could serveto replicatethese findingsas part of the ongoing refinementof the MPQ. Pain descriptors;Sensation;Classification;MPQ; Decisionrule
and
I
categoriesas wellas an additional category.The sensorycategoryencompasses10subcategories: p
m
Becausepain is a subjective,private experience,languageoffers a usefulmethod of labelingthis phenomenon; apart from its value in mental representation, languagealso servesas a tool in the communicationof pain to others. Words may be used to convey multidimensionalproperties of pain, such as intensity, sensation,and affectivereaction,whichare of particular diagnosticvalue to clinicians. The first systematic attempt to incorporate verbal descriptors in pain assessment was the McGill Pain Questionnaire or MPQ (Melzack 1975),currently the most widelyused instrumentin pain research and practice. The MPQ is a self-reportinstrument that presents 78 pain dewriptors distributed across 20 subcategories (with an additional 6 words in the Present Pain Index); theseare further organizedinto thrm broad sensory, *C 7
7
e-mail:[email protected]. sun.edu.
‘
p
T S 0
S
c
and For example,the word contained within the subcategory whereas the word falls within the subcatego~. The implicationis that each word reflects a particular sensoryproperty of pain. The affectivecategory containswords such as and which are supposed to reflect negativeemotion and its autonomic properties. Finally, the evaluativecategory containswordsrangingfrom to e which reflect the overall intensity of pain. In addition, each word from each category has a rank value indicativeof the relativeintensityof pain implied. Psychometrically,the MPQ meets several important criteria. Adequate test-retest reliability has been demonstratedfor someof the word subcategories(Love et al. 1989)and internal consistencyhas been shown in the case of cancer patients (Graham et al. 1980).MPQ ratingshave also been found to be sensitiveto standardized stimuli (Klepac et al. 1981), and capable of discriminatingbetweenacute and chronic pain (Teman b
3
32
and Dar 1986),betweenfunctionaland organic aspects of pain (Leavittand Garron 1980)and betweenvarious pain syndromes(Metzacket al. 1986).Concurrentvalidity has been observed with visual analogue ratings of pain (Walsh and Leber 1983) as well as medication dosageand recoverytime (Van Buren and Kleinknecht 1979). The successof the MPQ is further establishedby its translation or adaptation for use in more than a dozen languages. These include many of the European languages and others ranging from Arabic to Japanese. Clearly, in spite of the linguisticrelativity, there is a common need for a.vocabulary of pain. There are indications, however, that the MPQ pain vocabulary can be refined. For instance, the factor structure of the MPQ has been unstable across studies. As reviewedby Femandez and Turk (1992),the pool of MPQ pain descriptorsgenerallyrevealsa sensoryfactor, and lessoften,an affectivefactor, but the evaluativefactor has been difficultto uncover.In severalfactor analytic investigations,two or more of the factors also have beenconfoundedwith on? another. This probablyarises from the underlyingproblemswith the selectionand organizationof the verbaldescriptorsof pain in the MPQ. Focusingon the sensorycategoryalone, many inconsistenciesmay be noted regarding the classificationof words into the 10 MPQ sensory subcategories (Fernandez and Boyle 1994;Towery and Femandez 1994). Employingcluster analysis,for instance, Reading et al. (1982)found that the word was a descriptorwhereasit had been classifiedas in the MPQ. The word was a descriptorof b in pain rather than as indicatedby the MPQ, and the word was indicative of rather than d as suggestedby the MPQ. Similarly, Clark et al. (1993)employedhierarchicalclusteringto come up with an expanded list of pain descriptors organized along a new set of dimensions.Hase (1992) recentlyturned to rational approaches for reclassifying the existingMPQ words into subcategoriesas well as changingthe labels given to certain subcategories. These recent departures are suggestiveof difficulties in the classificationof MPQ descriptors. First of all, several words have multiple meanings. The very first word on the list,f has been classifiedas since it impliesa periodicityof occurrence.On the other hand, it may also be classified within the b subcategoryby virtueof its referenceto visual phenomena.Other words suchas implyboth sensoryand affectivequalitiesand hencemay appear in different subcategories or even different categories altogether. This ambiguity of meanings also has been observedby Torgersonand BenDebba(1983)in their research on multidimensionalscalingof pain descriptors. It also may be noted that many of the words in the sensorycategory of the MPQ are metaphors of the ac-
tions producinginjury or pain. Thus, there is no physical sensationthat is intrinsicallyof a quality, or for that matter, a quality; and are merelyactionsthat can potentiallylead to pain. The word then would have little if any place in the vocabularyof a pain patient who had neverbeen stabbed before. Yet, because pain is often so difficult to describe,patients may resort to metaphors in an effort to communicatetheir experience. Additionally, some words in the MPQ are incomprehensible.In our clinical experience,the word often evokesquestionsfrom patients about its meaning.Similarly, a word that patients seek clarificationon. Yet, other words in the MPQ may be comprehensiblebut are rarelyendorsedbecausethey are only marginallyrelevantto the experienceof pain. In a meta-analysisof 51 studiesusingthe MPQ, Wilkieet al. (1990)found that of the 78 MPQ words that describe pain quality,only 19words were selectedby more than 20%of subjects.Many of the translations and adaptations of the MPQ also arrive at a substantial reduction in the numberof descriptorsas compared to the original Englishversion,thus raisingthe possibilitythat the (universal)vocabularyof pain is smallerthan that suggested in the MPQ. An ancillaryproblemconcernsthe labelsgivento subcategoriesof pain descriptors.Someof theselabelssuch as are not clearly differentiated from other subcategory labels such as Others such as may be misnomers; in the MPQ, pitted against and contains words like and rather than or f Therefore, the term may be more appropriatethan b Finally,it is contendedthat the subcategoriesof and are really dimensionsof pain, as in the multi-axialIASP Pain Taxonomy (Merskey 1986), rather than classes of pain descriptors.These dimensionscan be used in conjunction with any class of sensorypain descriptors;thus, it wouldmake senseto speakof a pain with a thermal property of that also is spatiallydefinablein terms of an anatomical site on the body and tempolally definablein terms of its continuous or episodicfeature as the case may be. In view of the above issues, more careful consideration needs to be given to the selectionof meaningfid pain descriptors and the labeling of associated subcategories.Furthermore, the intensityrankings of these descriptorsas suggestedin the MPQ are in need of replication. In attemptingthesedual tasks, the present study focuses exclusivelyon the sensory descriptors of the MPQ. This category accounts for the bulk of MPQ descriptorsand has beenwidelyvalidatedin factor analytic investigations.Moreover, it is the sensation that definesthe intrinsicphysicalqualityof the pain whileaffectis primarilya reactivecomponentof pain. Through
33
the extraction of unambiguousdescriptorsof pain sensation and confirmation of the intensity values, languagecan be used more accuratelyin the qualitativeand quantitativeassessmentof pain. This process is undertaken in viewof Melzack’s(1975)invitation for further research and refinementof the MPQ.
1 D
Subjects A total of 70 students from an undergraduateclass in health psychologyat Southern Methodist Universityparticipated in the study. Subjectswere betweenthe ages of 17and 27 and reportedlyin good physicalhealth. P
Participationin the studywas a course requirementfor whichsubjects receivedthree points towards their course grade. Rules of informedconsent were adhered to and subjectswere free to withdraw without ~nalty. AHsubjectswere presentedwith a list of 84 pain descriptorsfrom the McGill Pain Questionnairewhich were to be classifiedinto sensory, affective,and evaluativecategoriesof the MPQ. The individual subcategory labels were not defined for subjects but were supplemented with the most representative example drawn from the descriptor list (on the basis of pilot data). Subjects were free to reclassifythe exampleitself, to classifywords into any subcategories, to add new words to the list, or to leave any word unclassified altogether. Apart from the c(assitication, subjects also provided numericalratings of intensity implied by each descriptor. This was donein referenceto a rating scalerangingfromO(no pain)to 10(maximumpain). D
P
Cutting Lacerating Comtrietive
66 42
a
Giventhe exclusivefocus on descriptorsof pain sensation,tbe frequencywith whicheach word appeared in each sensorysubcategory wastallied.A three-stepdecisionrule wasthen appliedto the frequency data to determine which pain descriptors related to each subcategory:(i) the absolute frequencywith whicha word was assigned to a subcategoryhad to exceedthat expectedunder a binomialprobabilityof 0.01;based on this, the minimumfrequencyrequiredwas 10; (ii) the relativefrequencythat a word was assignedto a subcategory (over atl alternative subcategoriesused) had to exceed 1/2;(iii) when a word met criteria for more than one subcategory,it was granted membershipin the subcategoryit wasmost frequentlyassignedto (the mode);however,when a word was bimodallydistributed across two subcategoriesit was considered ambiguousand therefore excluded. The combinationof the three criteria above was applied order to reach a decision regarding which words tit best into which s categories. In addition, means were computed for intensity ratings givenfor each word withineach subcategoryit had heen assignedto.
B
30
Using this conservativedecision rule, it was found that 32out of a total of 84 MPQ descriptorsmet criteria for classificationin the 10sensorysubcategories(Table I). This further means that 23 of the 55 (supposed)sensory descriptorsin the MPQ failed to meet criteria for inclusionin any singlesensory subcategory. Fig. 1 illustrates the 10 most frequently assigned words for each subcategory. However, many of these wordsattained frequenciesof lessthan 10,and so based on the binomialformula (criterion 1)theseobservedfre-
quencieswere not significantlydifferent from chance. For example,in the subcategory,the words p and attained frequenciesof 6, 7, and 8, respectively,and thus wereexcluded.Similarly, in the subcategory,three words and pinching)wereidentifiedfor exclusion,and for the subcategoriesof and at
34
Temporal ,
b
~ b J .
q &
I
l s
p
t 8
10
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30
40
SO
60
0
;Q
10
xl
30
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50
60
70
W
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Punctate Pressure c h s , p ,
1~I I
s !
v L
a
s s
o
10
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30
40
50
60
70
0
F
10
24
30
40
50
60
;O
i
C
60
70
F
C r
f
l
S
“
U 0
10
24
30
40
50
60
F
B .
S
I
a
b
s r m L , , .
Fig. 1. The frequencyof assignmentof words across subcategories.
l
35
leasthalf of the words warranted exclusionon the basis of this criterion. Having met the criterion of absolute frequency, membership in a subcategory also required that a descriptorhad to be assignedto that subcategoryin at least 5 of instancesas compared to its assignmentto all alternative subcategoriesused (criterion 2). For example,the word p attained an absolutefrequency of greater than 10in both the subcategoriesof p and i but had a relativefrequency of 0.33 in the latter subcategory and 0.51 in the former subcategory;in viewof this it was deemedmore appropriate as a descriptorof p Table I summarizesthe relative frequencies of all words that met criteria 1 and 2. The third and final criterion that all words had to satisfy for membership in a subcategory was that of unimodality.In other words, descriptors that attained suftlcientlyhigh absoluteand relativefrequencies,could not be bimodallydistributedacrosssubcategoriesif they wereto be granted membershipin a singlesubcategory. For example, the word l met both criteria 1 and 2 for i and p subcategories(Fig. 2). Therefore,it was deemedambiguous and excluded.Words such as andjlashing (Fig. 2) were also bimodalin their distributionand consequentlydeniedmembershipin any singlesubcategory. The final list of descriptorsthat met criteria for indi-
vidual subcategoriesof pain sensation are presented in Table I. On the average, three words emerged in each subcategoryas compared to the average of four words within subcategoriesof the MPQ. The actual classification of thesewords departed minimallyfrom that in the MPQ. For example, the descriptors within the subcategoriesof and wereidenticalto those in MPQ subclasses7 (thermal) and 19 (miscellaneous). For the and subcategories,notwithstandingthe few words excluded,all words retained matched those in the MPQ subcategories.The subcategoriesof s and contained some of the original words from corresponding MPQ subcategoriesas wellas new words which in all casescame from the MPQ miscellaneousgroups. The subcategorywasthe onlyonewhichcontainedan altogether new set of words;these words also had been previously designatedas miscellaneousin the MPQ. Finally,mean intensityratingsof each classifiedword are listed in Table I. As shown, individual descriptors withineach subcategorydiffer in terms of their implied intensityand could be rank-ordered accordingly.More importantly, the intensity ratings of this final set of wordsweresignificantlycorrelatedwith those originally reported by Melzackand Torgerson (1971) = 0.91, P <
0
Lancinating
Tearing
Hotness
O
4
4
Flashing
Numb Others
s
s
Brightness 35%
Fig. 2. ‘Lancinating’,‘Tearing’,‘Numb’,and ‘Flashing’as classifiedacross subcategories.
36
D
Proceedingfrom the research of Melzackand Torgerson (1971) and Melzack (1975), the present study investigatedthe classificationand intensity ratings of pain descriptorswithin a sample of universitystudents conversantin the Englishlanguage.However,the samplesizeof subjectsperformingthe classificationtask was considerablylarger in this study. The classificationtask itselfwas more stringentin that subjectsactuallyhad to assignwords to subcategoriesrather than merelyagree/ disagreewith the preexistingclassification.In rating the intensity of pain suggestedby each word, an interval scalewas used instead of a categoricalscale. Despite the above methodological departures, the findingsof this studyare remarkablyconsistentwith the originalorganizationof MPQ descriptorsof pain sensation, but they do providegroundsfor streamliningthese descriptors. Specifically,about 60Y0of the descriptors appearing in sensory and sensory-miscellaneous categoriesof the MPQ were retained, leaving23 words to be excludedbecauseof failure to meet the polythetic criteria of this study. First of all, somewords were not assignedfrequently enough to any subcategoryas to permit a rejection of the null hypothesis of random assignment.The word was among the very lowest in frequency, and therefore an underused word. This may be attributable to the failureof many subjectsto comprehendthe word or to grasp its relevanceto the communication of pain. Likewise,we have observed that pain patients have notable difficultyin understandingsuch words or relating them to pain. Such words are best excluded. Other wordswarranted exclusionbecauseof their low relative frequencies of assignment to any single subcategory.For example,the word appeared more than 10 times in the subcategory,but this accounted for less than 50% of the instancesin which it was assigned across all subcategories.By implication, t not reliably linked to temporal features of pain (or for that matter any other sensory property of pain); therefore, it was excludedfrom the final list. Thosewords that attained a suftlcientlyhigh absolute frequencyand relativefrequencybut were more or less equally distributed across more than one subcategory werenot retained.This is consistentwith Torgersonand BenDebba’s findings (1983) that some MPQ pain descriptorsare not definitiveof pain quality. Common in usage though they may be, these descriptors lack specificityof meaningand thus confound the interpretation of pain. Therefore,wordssuch as numbandflashing were excludedaltogether.The word was found to connote either coldness or dullness, while the word j wasfound to refer to either b or aspects of pain. Because of the high degree of ambiguitywhich detracts from the discriminantutility
of such words, they were not includedin the new set of descriptors. Conversely,the 32 words which met all criteria for retention were used frequently and unambiguouslyin the communicationof pain. These words represent a subsetof the originalMPQ descriptors,but their precise placementin individualsubcategoriescloselyresembles that laid out in the MPQ. Nearly all the new words in the subcategoriesactuallycame from the miscellaneous class of the MPQ suggestingthat several descriptors previously viewed as ambiguous in fact could be classified. Apart from the similarity in classification, the retained descriptors also correlated highly with the MPQ in termsof intensityratings.This representsa replicationof the seminalfindingby Melzack and Torgerson (1971)that verbaldescriptorscan be used reliablyto differentiatenot only among the qualitative aspects of pain but also to discern quantitativevariations in pain. It also adds to the levelof confidencein the diagnostic specificityof the new set of descriptors. Consequently, clinicianscouldmakeinferencesabout the sensationand underlyingpathology of pain as well as its magnitude. In short, this study suggestsa new subsetof pain sensation descriptors that excludes several words on the grounds of infrequencyand ambiguityof usage, yet retains most of the words from the original list in the MPQ, preservesmuch the sameorganizationof theseretained words across subcategories,manages to classify many words that were once left unclassified,and also replicates pain intensity ratings implied by each word retained. The end result is a more parsimonious collectionof descriptorsof pain sensation.In achieving this end, the present study has followed the direction started by the MPQ and the vision expressed by its authors for the continuedrefinementof the languageof pain. Future researchmight address the replicabilityof the presentfindingsin the population of pain patients who are the most likely users of pain descriptors. Crosslinguistic studies may be undertaken to assess the generalizabilityof thesefindings.Finally,sincethe present studywas confinedto descriptorsof pain sensation, it is necessaryto expandthe scopeof inquiryto affective descriptorsof pain as well. R Clark,C.W., Fletcher,J.D., Janal, M.N. and Carroll, J.D., Hierarchicalclusteringof 270descriptorsinto a pain, suffering,and pleasure space;their relationshipto the McGill Pain Questionnaire.In: B. Brommand J. Desmedt(Eds.),Pain and the Brain:From Nociception to Cortical Activity, Raven Press, New York, 1993,pp. 319-330. Femandez, E. and Boyle,G., A reconsiderationof the languageof pain with reference to the McGill Pain Questionnaire, Paper
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Melzack,R. and Torgerson,W.S., On the languageof pain, Anesthesiology,34 (1971)50-59. Merskey,H., Classificationof chronic pain: descriptionsof chronic pain syndromesand definitionsof pain terms, Pain, Suppl.3 (1986) S21-S225. Reading,A.E., Everitt, B.S. and Sledmore,C.M., The McGill Pain Questionnaire: a replication of its construction, Br. J. Clin. PsychoI.,21 (1982)339-349. Teman, B.H. and Dar, R., Physicianratings of pain descriptors:potential diagnosticutility, Pain, 26 (1986)45-51. Torgerson,W.S. and BerrDebba,M., The structure of pain descriptors. In: R. Melzack (Ed.), Pain Measurementand Assessment, Raven Press, New York, 1983,pp. 49–54. Towery, S. and Femandez, E., Describing pain sensations: MPQ wordsbased on a new decisionrule, Paper presentedat the Thirteenth Annual ScientificMeeting of the American Pain Society, Miami, 1994. Van Buren,J. and Kleinknecht,R.A., An evaluation of the McGill Pain Questionnaire for use in dental pain assessment, Pain, 6 (1979)23-33. Walsh, T.D. and Leber, B., Measurement of chronic pain: Visual analog scalesand McGill Melzackpain questionnairecompared. In: J.J. Bonicaet al. (Eds.),Advancesin Pain Researchand TheraPY, Vol. 5, Raven Press, New York, 1983,pp. 897-899. Wilkie,D.J., Savedra,M.C., Holzemer,W.L., Tesler, M.D. and Paul, S.M., Use of the McGill Pain Q m pain: a meta-analysis,Nurs. Res., 39 (1990)36-41.