A comparison of the Faces Pain Scale and the Facial Affective Scale for children's estimates of the intensity and unpleasantness of needle pain during blood sampling

European

Journal

of Pain (1999) 3: 301-315

A comparison of the Faces Pain Scale and the Facial Affective Scale for children’s estimates of the intensity and unpleasantness of needle pain during blood sampling Belinda Goodenough*,t, Katinka van DongenS, Nanda BrouwerS, Huda H. Abu-SaadS and G. David Champion* *Pain Research Unit, Sydney Children’s Hospital, Randwick, University of New South Wales, Sydney, Australia; #School Maastricht University, The Netherlands

Australia,- tSchool of Paediatrics, of Nursing Science,

To what degree can facial expression scales help children differentiate between the sensory and emotional aspects of the pain experience? This study examined the relationship between children’s ratings on the Faces Pain Scale (an intensity measure), the Facial Affective Scale (an affective measure), and a paired mechanical visual analogue (MVAS) method for measuring the intensity and unpleasantness of pain. It was predicted that ratings on the Faces Pain Scale should correlate best with the MVAS measure of pain intensity rather than unpleasantness. Likewise, ratings on the Facial Affective Scale should correlate best with the MVAS measure of pain unpleasantness (assumed to reflect an emotional dimension) rather than intensity. Eighty children scheduled for blood sampling were selected in two age groups: 4 to 6, and 7 to 10 years. Children rated needle pain using each pain scale. As hypothesized, ratings on the Faces Pain Scale correlated more highly with the MVAS ratings for intensity (rz0.77) than for unpleasantness (r=0.52). A smaller reverse finding was confirmed for the Facial Affective Scale which correlated more highly with the MVAS for unpleasantness (rz0.64) than for intensity (rz0.51). Factor analysis indicated that ‘pain dimension’ (intensity vs affect) was a relatively weak factor as compared with shared instrument variance (two MVAS vs two face scales). No systematic age effects were observed. In conclusion, the Faces Pain Scale and the Facial Affective Scale may partly measure different aspects of the pain experience in children, although it remains to be determined to what degree the obtained differences are clinically meaningful. 0 1999 European Federation of Chapters of the International Association for the Study of Pain

INTRODUCTION It is increasingly recognized that a comprehensive paediatric pain assessmentwill distinguish between a child’s sensory and emotional reaction to a painful event. Not only is this Paper received 15 April 1999 and accepted in revised form 9 July 1999. Correspondence to: Dr Belinda Goodenough, Pain Research Unit, Sydney Children’s Hospital, High St, Randwick, NSW 2031, Australia. Tel: +61 2 93821585; Fax:+61 2 93821580 Email: B. [email protected]

1090-3801/99/040301 + 15 $12.00/O 0 1999 European Federation of Chapters

consistent with the widely accepted definition of pain as an unpleasant sensoryand emotional experience (Merskey & Bogduk, 1994),but there is also evidencethat the sensory and affective dimensions may have differing neurophysiological foundations (e.g. Melzack, 1986).Important clinical implications for separating the two dimensions ire also indicated.

approach

of the International

From

work

with

adults,

the efficacy

of non-

pharmacological approaches is maximized when targeting affective rather than sensory features of pain (Malone et al., 1989;Dahlgren et al., 1995). With respect to children, it has

Association

for the Study

of Pain

302

8. GOODENOUGH

ET AL.

(4

(b) A

J$ 0 .04 F I 2

.A ,A&.

r, 0

0

.75

Fig. 1. Facial expression scales used in the study Scale (PA McGrath et a/., 1985; PA McGrath, 1990)

.85

(a) Faces Pain Scale

already been shown that non-pharmacological techniques, such as guided imagery and relaxation methods, can help decreasethe emotional distress associatedwith various therapeutic and diagnostic interventions, including the fear of pain (Ross & Ross, 1988;Kuttner, 1996). Given the growing clinical needfor the distinction between sensory and emotional responses, the question arises as to what degree facial expression scales can help children to estimate pain intensity independently from pain-related distress (affect). Facial expression scales are a widely accepted age-appropriate method for obtaining self-report ratings of pain from children at least as young as 34 years of age (Kuttner & LePage, 1989; PJ McGrath et al., 1995;Champion et al. 1998).Yet many published facial expression scales appear to confound the European

Journal

of fain

(1999),3

.97

(Bieri

et a/., 1990); (b) Facial Affective

depiction and potentially the measurement of sensory and affective responses (Chambers & Craig, 1998; Champion et al., 1998). For example, the presenceof tears on the ‘extreme pain’ face may have implications for different age groups of children, such as prompting an older child not to select that face to estimate pain intensity becayse the tears are interpreted as implying an equally intense emotional reaction to the pain or ‘acting like a baby’. The present research contrasts two facial expression measureswhich purport to measure, to some degree, different aspects of the pain experience. The Faces Pain Scale (Bieri et al., 1990) was developed as a 7-point unipolar measure of pain intensity ranging from ‘no pain’ to ‘most pain possible’ (see Fig. la). By way of contrast, the Facial Affective Scale (PA McGrath

COMPARING

FACIAL

EXPRESSION

SCALES

FOR RATING

NEEDLE

et al., 1985), was developed as a more broad bipolar 9-point measure that encompasses a child’s emotional (affective) reaction to a pain experience ranging from ‘happiest feeling possible’ to ‘saddestfeeling possible’ (seeFig. 1b). To date, thesetwo facial expressionscaleshave been used in many separatestudies of pain self-report in children (e.g. Arts et al., 1994; PA McGrath, 1990)but have not been directly compared with respectto ratings of the same pain. The aim of this study was to examine the relationship between children’s ratings on the Faces Pain Scale, the Facial Affective Scale, and a paired visual analoguemethod for measuring the intensity and unpleasantnessof needle puncture pain during blood sampling in children aged4 to 10 years. The paired mechanical visual analogue scale (MVAS) paradigm was developed by Price et al., (1994) in studies of experimentallyinduced pain in adults. With careful instruction, many children as young as 334 years of age can apply the method to estimate the intensity of pain (how much they hurt) as distinct from how unpleasant (bothersome, distressing, ‘yucky’) the pain felt (Goodenough et al., 1999). An advantage of the method is that significant differences between intensity and unpleasantness ratings using the paired MVAS paradigm are unlikely to be explained by method variance. The principal hypothesis of the study was two-fold. Firstly, it was predicted that the Faces Pain Scale,as an intensity measure,should correlate best with the visual analogue measure of pain intensity rather than unpleasantness.The corollary hypothesis was that ratings on the Facial Affective Scale, assumed to reflect the emotional rather than sensorydimension of pain experience,should correlate best with the visual analogue measure of pain unpleasantnessrather than intensity. Children were sampled in two age groups (46 years, 7-10 years). The study was exploratory with respectto investigating whether an age difference would significantly impact upon these hypothesized interscale correlations. Based on previous work, however, showing that children younger than 7-8 years of age show smaller differences between intensity and unpleasantness ratings of venipuncture pain (Goodenough et al., 1999), it was expected that

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ratings on the two facial expressionscalesmay be more highly correlated in the younger of the two agegroups (46 years) in the presentstudy. In addition to the previous hypotheses,a secondary aim of the study was to examine the degree to which a range of measurable factors predicted the separatevariance in ratings on the four pain scales. It is well-established that a major predictor of the variance in needle pain ratings from blood tests in children is chronological age (Fradet et al., 1990; Goodenough et al., 1997, 1999; Arts et al., 1994; Fowler-Kerry & Lander, 1987, 1990; Lander & Fowler-Kerry, 1991).The present study affords the opportunity to examine the extent to which agepredicts variance on four different pain measures,as well as the degree to which other factors account for additional variance once agehas been controlled for. Within the constraints of the study design, the factors of interest included needle history variables and indices of family structure.

MATERIALS

AND METHODS

Subjects

The participants were children 4-10 years of age, sampled in two age groups (4-6 years, 7-10 years), who were consecutively scheduled for a blood-sampling procedureat the Prince of Wales Pathology Outpatients Department (venipuncture) or the Sydney Children’s Hospital Outpatients Haematology Clinic (finger-prick). In total, 95 children were invited to participate. The parents of four children did not provide consent, and data for 80 of the remaining 91 consenting families were admitted to the study after meeting the following criteria: (a) The first language for the family was English (to understand the scales and complete a questionnaire). On this criterion, two children were excluded on the basis of poor English comprehension by their parents. (b) No topical anaesthetic preparation had been applied to the potential needle site. On this criterion, five children, all venipunctures, were excluded for using EMLA cream. European

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TABLE

1.

Demographic

characteristics

of the subject

sample.

4 to 6 year olds

n Finger Prick Male Female Venipuncture Male Female Full Sample

SE,standard

20 7 13 21 11 10 42

Mean age (SE) 5.1 5.3 5.0 5.1 5.1 5.0 5.1

1.2) (.3) (.2) l.2) l.3) (.3) (.I)

7 to 10 year olds

No. prior needles (SE)

Days since last needle (SE)

n

164 (27) 164 (48) 164 (35) 60 (30) 97 (57) 19 (7) 111 (22)

52 (12) 94 (27) 30 (7) 199 (56) 293 (97) 96 (27) 129 (198)

19 9 10

and concepts as per the standardized interview used by investigators when collecting self report ratings (see Materials). On this criterion, two children (in the 7-10 years age group and scheduled for venipuncture) refused to provide ratings using one or more of the measures, and one child was not included after stating that opening a birthday present was painful (seeMaterials). Only one needle insertion attempt was required. The data for four children (all venipuncture) were excluded from the analysis after the pathology technician indicated that two attempts at needle insertion were required.

For the final sample of 80 children whose data were admitted to the study, the demographic characteristics concerning mean age, sex, needle type, and estimates of factors associated with previous needle-relatedprocedures are shown in Table 1. Materials Pain Measures

(a) FacesPain Scale(Bieri et al., 1990),FPS (see Fig. la): this measure comprised sevenfaces depicting increasing gradations of pain severity, from ‘no pain’ on the extreme left face, to ‘most pain possible’ on the extreme right face. The child chose a face to indicate the level of pain intensity, which was converted to a numerical score from 0 to 6, European

Journal

20 10 10 39

Mean age (SE) 8.6 8.7 8.7 8.5 8.5 8.5 8.6

t.31 (.3) (.4) (.3) (.4) (.4) (.I)

No. prior needles (SE) 273 172 363 46 63 29 156

(101) (55) (186) (15) (27) (14) (53)

Days since last needle (SE) 92 90 93 452 130 773 276

(33) (52) (45) (172) (45) (316) (93)

error

cc>The child understood how to apply the scales

(4

ETAL.

of Pain

(1999).

3

where 0 represented ‘no pain’ and 6 represented ‘most pain possible’. This scale has been shown to be adequately understood by young children and with satisfactory evidenceregarding its reliability, validity and preliminary ratio scaling properties (Bieri et al., 1990). (b) Facial Affective Scale (PA McGrath et al., 1985;PA McGrath, 1990),FAS (seeFig. lb). This scalecomprised nine faces ranging from ‘happiest feeling possible’ to ‘saddest feeling possible’. The child was told that the faces showed how a person could feel, and was asked to select the face that best represented how unpleasant their pain felt. Based on pilot interviews with parents and children and our previous research (Goodenough et al., 1999), for children who did not fully comprehend the meaning of the word unpleasant, the term ‘yucky’ was found to be the closest emotive synonym for in the sense of ‘bothersome and horrible’ for samples of Australian children. In this study, the presentation format of the Facial Affective Scale was the randqmized 3-by-3 pattern used by PA McGrath as part the formal pain assessment interview at the Children’s Hospital of Western Ontario (PA McGrath, 1990; see Appendix). This randomized version was adopted in the present study in order to reduce the possibility for children trying to match the relative position of chosen faces across the two facial expression measures (both of the scales move from left to right with respect to the extreme pain relative to a

COMPARING

FACIAL

EXPRESSION

SCALES

FOR RATING

NEEDLE

neutral or ‘no pain’ value; see Fig. 1). Research has shown that the random and fixed ordered bipolar formats of the Facial Affective Scale to be equivalently valid and able to be used in a clinical situation (PA McGrath et al., 1985, 1996).No tested randomized pattern of the Bieri et al. FacesPain Scalefor clinical usewas available.The Facial Affective Scalewas scored using the affective magnitude ratings assignedto each face (see Fig. l), as derived from estimates by children as young as 3 years of age (PA McGrath et al., 1985). (c) Mechanical Visual Analogue Scale for pain intensity (Price et al., 1994) MVAS: this scalewas a 15 cm plastic device with a central slider covering a region of red colour. The endpoints were ‘no pain sensation’ (left) and ‘most intense pain sensationpossible’ (right). As the slider was pulled from left to right, it progressively uncovered the zone of red colour. In line with previous research using the scale with children (Goodenough et al., 1999),the child was shown how the scale was mechanically manipulated, with the amount of uncovered red colour equalling pain. The child was askedto pull the central slider from left to right to uncover the red to show how much the needlehurt. By turning the device over, the selectedposition of the slider was converted to a score,within a single decimal place, from 0.0 (no pain) to 10.0(most pain). (d) Mechanical visual analogue scale for pain unpleasantness, MVAS: this scale was identical to that described above for the MVAS for pain intensity, except that the endpoints were redefined as ‘not at all unpleasant/yucky’ (left) and ‘most unpleasant/yucky sensationpossible’ (right). Administration of the mechanical visual analogue scales required a basic initial assessment for comprehension of the concept of unpleasantness as well as understanding how to apply the visual analogue concept. In line with previous work using this scale with children rating venipuncture pain (Goodenough et al., 1999) a standard dialogue was employed. For those children who appeared not to initially comprehend the word ‘unpleasant’, the synonym ‘yucky’ was

305

PAIN

substituted. In this standard dialogue, the child was initially asked to use the MVAS to rate how much it would hurt to fall and scrapetheir knee, and how much it would hurt to open a birthday present. If the child rated opening a birthday present as painful, then that child’s data were excluded from the analysis-it was assumedthat the child either could not sufftciently understand the distinction between intensity and unpleasantness,or could not sensibly apply the MVAS concept to rate an internal state. The data for one child (a male in the 4-6-year-old category for venipuncture) were excluded on this basis. Following this initial question, the dialogue continued such that the child was asked to give an example of (a) something pleasant, (b) something unpleasant, (c) something painful, (d) something unpleasant that does not really hurt, and (e) something that hurts but is not really unpleasant. Questionnaire

As in previous research(e.g. Goodenough et al., 1999) parents completed a standardized questionnaire to provide additional demographic data (e.g. height, weight and position in the family) and information relevant to the child’s experience of needles.For the latter, the parent was asked to provide quantitative estimates of the child’s needle history (number of needles; last needle type; days since last needle; whether the child had watched a family member receiving a needle);as well as their own experiencewith needles (whether the parent usually gets anxious prior to receiving a needleand if their child knew how the parent felt about needles). Procedure

The pain rating scalesand the questionnaire were administered by the same two investigators (authors NB and KvD), who approached the parent and child in the waiting room area of the relevant clinic. After informed consent was obtained, the parent, if there was time, began to complete the demographic questionnaire. No questions were asked of the child (for this study, institutional ethics guidelines and concerns on European

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patient compliance prevented investigators from interviewing the child about the upcoming needle, specifically expectations for pain and levels of pre-procedural anxiety). When the child’s turn for blood sampling came around, both of the investigators accompanied the family to the consultation room or designated cubicle area where the blood test was to be performed. All linger prick procedures were performed in the outpatients haematology clinic, whilst all venipunctures were performed by a registered paediatric nurse in the pathology outpatients department shared by Prince of Wales and Sydney Children’s Hospitals. The linger pricks and venipunctures proceeded in the routine fashion, with the investigators remaining present and observing the procedure from an unobtrusive distance and completing notes as necessary. After the blood test was completed, and within 5 min of the procedure concluding, one of the investigators collected pain ratings from the child while the second investigator remained with the parent, who completed the demographic questionnaire. The only deviation from this practice occurred when only a single investigator was available to administer the measures (e.g. dual page to both clinics), and therefore spoke to the child first and while the parent was occupied completing the questionnaire. This was the case for 15 children (4 lingerpricks and 11 venipunctures). With respect to the child’s self report, the four pain scales were always administered in the same order: Faces Pain Scale, MVAS-intensity, Facial Affective Scale, MVAS-unpleasantness. This fixed administration order reflected the fact that institutional ethics guidelines did not permit the investigator to talk to the children about needle pain before the procedure. Thus, each child had to be instructed on how to use a scale immediately prior to applying it to rate actual pain. To facilitate this process, the scales were administered in an order that seemed to best help the child to understand the concepts to be measured as well as to use the scale appropriately. The Faces Pain Scale was deemed by the investigators to be the easiest and the analogue scale for unpleasantness, MVAS-unpleasantness, potentially the most difficult. The pathology technician provided a rating as to the relative European

Journal

of Pain (1999),

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GOODENOUGH

ETAL.

difficulty of access using the categories ‘easy’, ‘moderate’ or ‘difficult’, and the number of attempts required to obtain the blood sample. If there was more than one attempt to insert the needle, then the child’s data were not admitted to the analysis (this was the case for four venipuncture patients).

Data analysis In addition to standard analysis of variance techniques, differences between pairs of (Pearson) correlations related to hypothesis testing of interscale relationships were examined using Hotelling’s Tz formula for comparison of related samples (Hotelling, 1940). Exploratory factor analysis was used to examine the underlying factor structure for the four self-report ratings. Hierarchical multiple regression analysis was used to test for effects of age and other variables of interest in predicting the variance in ratings for each of the pain measures. Given the typical positive skew of needle pain ratings toward the low pain end of rating scales, especially for older children, interscale relationships were also examined using distribution-free (non-parametric) tests (Spearman correlations and Wilcoxon signed rank). These non-parametric tests will only be reported to clarify outcomes of the previously described parametric statistical techniques.

RESULTS Sample

characteristics

As indicated in Table 1, the sample of children undergoing blood test via linger-prick were estimated (by their parents) as having received significantly more previous needle-related procedures than the venipuncture sample (see Table 1) [F(1,79)=9.25, p=O.O03] and also as having experienced their last needle relatively more recently [F(1,79)=7.94, p=O.O06]. This latter lmding reflects the fact that all of the children in the finger prick sample (all from the haematology clinic) were receiving blood tests with some regularity to monitor treatment for a diagnosed

COMPARING

FACIAL

TABLE

Mean

2.

EXPRESS/ON

ratings

range:

Finger-prick 4-6 years 7-l 0 years Venipuncture 4-6 years 7-10 years Full sample 4-6 years 7-10 years MVAS, JCMechanical

SCALES

FOR

RATING

NEEDLE

307

PAIN

on each of the four pain measures,

as a function

of needle

type and age group

MVAS

MVAS unpleasantness O-IO

Faces pain O-6

Facial affective 0.04-0.97

intensity O-IO

Mean

SE

Mean

SE

Mean

SE

Mean

SE

1.90 2.75 1.00 2.07 2.62 1.50 1.99 2.68 1.26

0.36 0.57 0.34 0.04 0.56 0.45 0.26 0.40 0.31

0.59 0.64 0.54 0.63 0.69 0.57 0.61 0.66 0.56

0.05 0.07 0.07 0.04 0.06 0.06 0.03 0.05 0.04

2.28 3.39 1.12 2.66 3.61 1.66 2.47 3.50 1.39

0.44 0.76 0.24 0.52 0.76 0.65 0.34 0.53 0.35

2.65 3.18 2.09 3.24 4.47 1.95 2.95 3.84 2.02

0.48 0.74 0.59 0.55 0.80 0.65 0.37 0.55 0.44

Visual

Analogue

Scale;

SE, standard

illness (e.g. juvenile diabetes), while for the venipuncture sample (all from the general pathology outpatients), proportionally more of the children were undergoing blood tests for diagnostic purposes or for monitoring of treatment effects that required a larger volume of blood for multiple testing (e.g.oncology). For the majority of children (78% of venipuncture subjects, 82% of the tinger-prick subjects), their last needle-relatedprocedure was also a blood test. No effects or interactions involving age or sex were found in these demographic variables. All children were accompanied by at least one adult: mother alone, (41%), father alone (ll%), both parents (15%), mother with other adult (24%), father with other adult (5%), or both parents with another adult (4%). Chi-Square analysis showed that the form of adult accompaniment did not differ as a function of the child’s age, although fathers were more likely to accompany the child alone if the blood sampling required fingerprick, whilst mothers were more likely to bring another adult friend in the venipuncture group [x2(5)=12.377p=O.O30].

Pain ratings

The mean ratings for each of the pain measures, and for each of the agegroups, are listed in Table 2. Whilst pain ratings from children in the venipuncture sample were slightly higher than those from the finger prick sample (seeTable 2),

error

analysis of variance (ANOVA) revealed no significant differences in mean ratings as a function of needle type for any of the measures. Therefore, given that the focus of the present researchwas to examine within-subject variance in the use of different measuresof pain, rather than between-group variance for different types of needles,in order to simplify the reporting of the main analyses, unless otherwise stated, the data are reported as collapsed acrossneedle type. The responsedistributions for each of the four measures and for each age group are shown in Figure 2. Compared with the younger age group, the children in the older agegroup generally provided ratings which had a greater positive skew (i.e. toward the no/low pain anchor points on the scales). The 4-6 year olds also appeared more likely than the older age group to select the extreme pain value on a given scale, especially when using either of the two facial expression scales.Analyses of variance confirmed that the effect of age was significant for the Faces Pain Scale [F(1,79)=8.001, p=O.O06], the MVAS for intensity [F(l,79)=10.059, p=O.O02], and the MVAS for unpleasantness [p(l,79)=6.293, p=O.O14],but just failed to reach statistical significance for the Facial Affective Scale [J’(1,79)=3.004,p=O.O87].There were no signiticant main effectsor interactions involving the sex of the child in these analyses. Due to the bipolarity of the Facial Affective Scale (it was the only measure in the present study that incorporated a graded series of European

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of Pain (1999),

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Fig. 2.

Response

frequency

distributions

for each pain measure,

--k-&q-&

” I i ki b ; A il ;o Age (years)

Fig. 3. Paired-MVAS results: mean self-report ratings for intensity (controlling for unpleasantness) and unpleasantness (controlling for intensity), plotted as a function of the child’s age

‘hap’py’ after the neutral ‘no pain’ anchor point), it was not possible to make direct comparisons of mean ratings on the four measures,even with the scores standardized. Concerning the paired MVAS paradigm, however, and following previous researchusing this method (Goodenough et al., 1999),covariate analysis of variance was used to obtain a finer investigation of the significant main effects of age in the unique variance on each of these two measures,beyond the two categories of age in the study design. In this European

Journal

of Pain

(1999).

3

comparing

Affective correspond

older

Scale

score*

with faces in Figure

and younger

1

children.

approach, MVAS-intensity scoreswere analysed with MVAS-unpleasantness ratings entered as a covariate, and vice versa. Chronological age was entered as a seven-level factor, corresponding with age in whole years from 4 to 10, and needle type (finger prick versus venipuncture) was also controlled for as a covariate.The adjusted means resulting from this ANCOVA approach are plotted in Figure 3. The results indicated that a significant age effect persisted for intensity ratings with unpleasantness controlled for [F(6,79)=3.001, p
relalionships

Averaged across age, the correlation (Pearson) between the Faces Pain Scale and the Facial Affective Scale was 0.46, and between the two MVAS measures the correlation was 0.79. Reflecting the thrust of the main hypotheses, Figure 4 compares the correlations for the Faces Pain Scale and the Facial Affective Scale with each of the MVAS measures of intensity and unpleasantness.As can be seen in Figure 4, the

309

COMPARING FACIAL EXPRESSION SCALES FOR RATING NEEDLE PAIN

TABLE 3. Interscale tion of age.

correlations

(Pearson)

as a func1

Facial Affective

MVAS intensity

MVAS unpleasantness

age:

4-6

7-10

4-6

7-10

4-6

7-10

Faces Pain Facial Affective MVAS intensity

0.43

0.44

0.74

0.73

0.49

0.43

-

-

.0.49

0.49

0.66

0.59

-

-

-

-

0.78

0.75

MVAS,

Mechanical

Visual Analogue

‘,I 0.8

Scale. 0

Faces Pain Scale correlated more strongly with the MVAS measureof intensity (r=0.77) than for unpleasantness (r=0.52). This difference was statistically significant according to Hotelling’s p [t(77)=5.45, pcO.051. The reverse pattern of results was evident for the Facial Affective Scale, which correlated more strongly with the MVAS for unpleasantness (r=0.64) than for intensity (r=0.51) [t(77)=2.29 pO.O5].This remained the casewhen non-parametric Spearman Rank order coefficients were calculated [t(36)=1.97, p>O.O5]. Exploratory factor analysis with oblique rotation was used to examine the underlying structure of the intercorrelations between the four pain measures.On inspection of the bivariate correlation matrix showing moderate-tohigh correlations between all possible pairs of scales,it was decided that eigenvectors accounting for at least 10% of the variance may be interpretable, with minimum factor loadings of 0.40 considered meaningful. According to thesecriteria, three eigenvectorsemerged, and the results of the analysis are summarized in Table 4. The factor accounting for the largest proportion (71%) of the variance may be described as reflecting shared instrument variance (i.e. the two facial expression scales vs the two MVAS

pa;;

Facial

Scale

TEE”

Fig. 4. Comparison of the relative Pearson correlations of the Faces Pain Scale and the Facial Affective Scale with the paired MVAS intensity measures of pain unpleasantness and pain intensity.

measures). A second factor explaining an additional 16% of the variance, seemedto be reflecting a singular contribution of the Facial Affective Scale. A third factor accounting for 10% of the variance appeared to be reflecting ‘pain dimension’, contrasting the two intensity measures (Faces Pain Scale, MVAS-intensity) against the two affective measures (Facial Affective Scale,MVAS-unpleasantness). Whilst the proportions of variance explained by Factors 2 and 3 were small, a post-hoc hypothesis was formulated with respect to the singular contribution for the Facial Affective Scale (Factor 2): the result may reflect the fact that the Facial Affective Scale is the only bipolar measure among the four pain measures (i.e. happy - neutral - sad). To check this interpretation, the factor analysis was repeated with a recoding of the Facial Affective Scale ratings into a 5-point unipolar measure of negative affect. In this format, the happy faces(A to E, see Fig. lb) were assigned the affective magnitude rating for the neutral face (0.59, no negative affect) while the remaining Faces (F to I) were unchanged. Data for 37 children required recoding in this manner (16 in the 4-6 years agegroup, and 21 in the 7-10 years age group). The results of this second factor analysis on the four measures and using the recoded version of the Facial European

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B.

TABLE 4. Results of exploratory factor analyses showing the rotated loadings along with eigenvalues and percentage of explained variance for each factor. Analysis Factor Eigenvalue Variance f%) Faces Pain Scale Facial Affective Scale MVAS-intensity MVAS-unpleasantness

1

2.85 71.4 0.01 0.03 0.72 0.96

Factor

1 2

0.63 15.7 0.10 0.96 -0.09 0.14

0.40 70.1 0.95 0.06 0.43 -0.011

3

Factor 2.99 74.9 0.01 0.06 0.72 0.93

1

ET AL.

for each of the four pain scales, Analysis

Factor

GOODENOUGH

2”

Factor 2 0.52 13.1 -0.92 -0.09 -0.45 0.12

Factor 3 0.37 9.3 0.13 0.94 -0.09 0.17

* Analysis 2, Facial Affective Scale recoded as a five- face unipolar negative affect measure. Note: only eigenvectors accounting for > 10% of the variance are reported, and loadings 5 0.40 were considered meaningful.

Affective Scale are included in Table 4. The overall proportion of variance explained did not differ greatly between the two analyses. In short, the main difference was simply the reversal of the order for the relative proportions of variance explained by the two weaker eigenvectors identilied in the original analysis (i.e. Factors 2 and 3)-probably reflecting the fact that the Faces Pain Scale correlated a little more highly with the 5-point recoded version of the Facial Affective Scale (r=0.54) than with the 9-point bipolar original version (rz0.46). Thus, there is a still a suggestion from the relative loadings in the second factor analysis for a weak factor representing ‘pain dimension’ (i.e. the two intensity measures vs the two affective measures), and a small residual of variance explained by a unique contribution of the Facial Affective Scale, albeit less than 10% of the total variance in the second factor analysis.

Predicting measures

variance

on individual

pain

Hierarchical Multiple Regression Analysis was used to explore the degree to which age, and several other variables of interest measured prior to the blood test, predicted the variance in ratings using each of the four measures. The aim of these analyses was to examine whether potential correlates of needle pain intensity ratings examined in previous research (Goodenough, 1997, 1998, 1999) accounted for different proportions of the variance in children’s pain scores (after age European Journal

of Pain (1999), 3

and needle type were controlled for) if the ratings were of unpleasantness rather than intensity, or derived from a facial expression rather than a visual analogue scale. Thus, the same model was tested for each of the four measures and comprised eight steps: (1) initial control for current needle type (venipuncture vs lingerprick); (2) child’s age; (3) body surface area and body mass estimates; (4) child’s sex; (5) needle history (type of last needle, and estimates of days since last needle and total number of prior needles); (6) family structure (number of siblings and child’s position in family); (7) information about parent (gender, does the parent get anxious about needles, does the child know how the parent feels about needles); (8) whether the child has watched a family member receive a needle. Whilst these regression analyses employed a lower subjectsto-variable (STV) ratio (approximately 6: 1) than convention (approximately 10: l), the current STV ratio was above the minimum of 5: 1 recommended for multivariate analyses (e.g. Grimm & Yarnold, 1995). In addition, the interpretative emphasis was on the hierarchical comparison of changes in explamed variance (r2) when forcing variable entry into an identical regression model for four different dependent measures, rather than the detection of atheorectical data-driven differences. The results of the four multiple linear regression analyses are summarized in Table 5. Overall, approximately 30% of the variance in ratings on the Faces Pain Scale, the Facial Affective Scale and the MVAS for unpleasantness, and nearly 50% of the variance in ratings on the MVAS for intensity could be accounted for.

COMPARING

FACIAL

TABLE

Results

5.

EXPRESSION

SCALES

of hierarchical

Scale: (Step)

FOR

multiple Faces

Variable

(I) Needle (FP/VP) (2) Age 0.19* (3) Body Surface Area Body Mass Index (4) Sex (5) Days since last needle Type of last needle Total no prior needles (6) No. of siblings Position in family (7) Parent gender Parent anxious? Know how parent feels? (8) Watched family member? F(14,65) &,, standardized P end, standardized * ~0.05 (note:

RATING

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regression

Pain

PAIN

analyses Facial

311

on pain ratings

Affective

MVAS

intensity

MVAS

unpleas

I$,

Pend

F

It”

Bmi

+

B I”

B e”d

6

Pi”

Bend

lJ

-0.04 -0.36"

-0.12 -0.42

0.01 0.13"

-0.07 -0.24*

-0.07 -0.16

0.01 0.06*

-0.06 -0.51"

-0.09 -0.30

0.01 0.27*

-0.09 -0.42'

-0.12 -0.26

0.01

-0.16 0.12 0.13 0.15 -0.03 0.19 0.20 0.10 -0.19 0.01 -0.07 0.17

0.02 0.01 0.06 0.11 0.01 0.26" 0.15 0.14 -0.18 -0.02 -0.11 0.17 2.04"

-0.37 0.30 0.07 0.17 0.08 0.24* 0.01 0.15 -0.15 0.21 0.10 -0.09

-0.34 0.20 0.01 0.24* 0.05 0.18 0.01 0.10 -0.14 0.23 0.14 -0.07 1.92*

-0.45 0.23 0.06 0.27" -0.13 0.05 0.10 0.13 -0.13 0.03 -0.10 0.26*

-0.32 0.15 -0.01 0.23* -0.07 0.13 0.05 0.18 -0.12 -0.01 -0.18 0.26* 4.27*

-0.27 0.18 0.05 0.22* -0.15 0.09 -0.02 0.04 -0.01 0.14 -0.06 0.09

-0.28 0.18 0.04 0.24* -0.09 0.11 -0.02 0.04 0.00 0.13 -0.09 0.09 1.97”

0.14 0.16

0.22 0.24

0.28 0.30

0.10 0.11

0.19 0.21

0.25 0.26

0.30 0.31

0.37* 0.40

0.43 0.48*

0.21 0.21

0.27 0.27

0.29 0.30

partial regression coefficient on step that variable was entered into model; partial regression coefficient on step 8 (after all variables entered), ?=R-Squared, for P, *denotes statistically significant change in ? since previous step in analysis).

This result appears to be largely attributable to the greater impact of the child’s age for the MVAS intensity scores (accounting for 26% of the variance) as compared with the other pain scales (especially the Facial Affective Scale, where age accounted for only an additional 5% of the variance). After the effect of age had been controlled for, there is little evidence for any of the remaining variables emerging as significant or dominant predictors for any of the four pain measures. Rather, each step of the analysis explained a further 24% of the variance, which generally proved not to be statistically significant individual increments in r2. There are perhaps only two exceptions. Firstly, there is some impact of needle history estimates (step 5). Whilst the combination of these needle history parameters yielded a significant change in r* only for the MVAS-intensity ratings, inspection of the standardized partial regression coefftcients after all variables have been entered does indicate some influence of the time since last needle on the scores from the Facial Affective Scale and the MVAS-unpleasantness, whilst it is the estimate of total number of needles that shows some predictive value for Faces Pain Scale scores. Secondly, for the MVAS-intensity ratings, higher scores appeared to be predicted by the child having watched a family member receive a needle (step 8).

DISCUSSION As initially hypothesized, the Faces Pain Scale showed a significantly higher correlation with a visual analogue measure of pain intensity rather than pain unpleasantness (see Fig. 4). Likewise, as predicted, the Facial Affective Scale showed the reverse pattern of results, correlating significantly more highly with the visual analogue measure of pain unpleasantness rather than pain intensity. There was no evidence for any significant influence of the child’s age on these correlational patterns (see Table 3). Therefore, the speculative hypotheses that younger children would show higher correlations between pairs of scales than older children are rejected, at least for ratings of brief acute (needle) pain. Whilst predictions were confirmed with respect to the interrelationships between the four pain measures, the correlations between pairs of scales purporting to measure different dimensions of pain remained strong. For example, the Faces Pain Scale correlated moderately and equally well with the two affective measures: the MVAS for unpleasantness (r=0.52) and the Facial Affective Scale (rx0.54). At least three sources of influence may underpin this result. The first is simply the likelihood for a substantial European

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B.

overlap between the intensity and affective dimensions of pain, not least of which is that physiological pain (even briefly from needles) may need to attain some level of intensity prior to the perception of its unpleasant or distressing qualities. Secondly, and related to the first, the measurementscalesthemselvesmay not be exclusively sensitive to either of the two constructs of intensity or unpleasantness.Thirdly, similar scale methodologies may yield similar magnitudes of ratings, irrespective of the pain dimension under scrutiny (i.e. shared instrument variance). It is likely that each of these three sourcesof influence contributed to all of the possible pairwise correlations betweenthe pain scales,and the outcome of the factor analysis on the four measures depends on this issue (Table 4). The underlying factor structure indicated that any difference reflecting unique measurement of pain intensity as opposed to pain-related affect was overwhelmingly subordinate to the impact of shared method variance. That is, the single dominant factor accounting for most of the variance (71%) in pain ratings contrasted the visual analogue and facial expressionmethods. In comparison, little more than 10% of the variance could be explained by comparing the two intensity measureswith the two affective measures.Thus, while there was a significant difference between the intensity and unpleasantnessratings as derived from the paired-MVAS method (e.g.Fig. 2), these two analogue measureswere still correlated best with each other (~~0.79)than with either of their facial expressioncounterparts (seeFig. 3). In this sense,the presentresults parallel studies in adults using a similar multitrait-multimethod approach: it has been shown that instrument variance can obscureevidencefor the differential assessmentof the sensory,intensity and affective dimensions of pain when using a battery of different scaletypes (Holroyd et al., 1996). Against the backdrop of moderate-to-high correlations between all pairs of pain measures (e.g. Table 3), the fact that the two facial expression scalescorrelated lesshighly with each other (u=O.54) than with each of the MVAS scales (Fig. 2) is impressive. It is also the case that this correlation between the two face scaleswas substantially less than the corresponding correlation European

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of Pain (1999),

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GOODENOUGH

HAL.

between the two MVAS scales (~~0.79). These results may partly reflect the deliberate attempt in the present study to reduce the similarity of the presentation format of the two facial expression scalesvia the randomized nine-face pattern for the Facial Affective Scale (PA McGrath, 1990;PA McGrath et al., 1996).It is also possible that the two face scalesare intrinsically different in their underlying constructs of measurement, as representedin the facial expressionsthat comprise the scales,rather than essentially the same type of scale presented with different instructions reflecting either the sensory intensity or affective unpleasantnessof pain. While the corresponding Eigenvector was weak, the results of the factor analysis did suggest that the Facial Affective Scalewas sufficiently different from the other three measures to provide some small unique contribution to the explained variance, originally approximating to 16% (see Table 4). This uniqueness is not readily defined, but may be partly attributable to the bipolarity of the Facial Affective Scale-the evidence for a singular contribution of the scale was diminished when scoreswere recoded as a unipolar scale of negativeaffect (seeTable 4). The possible role for this bipolarity factor should not be underestimated. Recent research shows significant influences of the representation of bipolarity as opposed to unipolarity of affect in facial expression scalesfor pain measurement,which also can be complicated by a child’s age, at least in the situation when children are rating hypothetical pain (Chambers & Craig, 1998). In the present study, the Facial Affective Scale was the only measure failing to show the conventional agemain effect for needle pain (e.g. Fradet et al., 1990;Goodenough et al., 1997, 1999;Arts et al., 1994;Fowler-Kerry & Lander, 1987, 1990; Lander & Fowled-Kerry, 1993).This is in keeping with other work showing that, irrespective of age effects on other measures, the Facial Affective Scale does not appear to be nearly so sensitive to agedifferences(PA McGrath et al., 1996).On the one hand, this may suggest that affective responsesto pain are not as age-dependentas responsesin the sensory intensity domain. It is certainly the case that, in keeping with previous work using the paired-MVAS method in children

COMPARING

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EXPRESS/ON

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FOR

RATING

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(Goodenough et al., 1999) the age effect persisted only for the MVAS-intensity and not the MVAS-unpleasantness ratings when only the unique variance in the measures was examined (Fig. 3). An alternative suggestion is that unipoiar scales in an ordered or continuum format with designated endpoints are those most likely to manifest age-related differences. In the present study, the Facial Affective Scale was the only scale which presented options in a randomized order with no endpoints specified-a child was simply asked to indicate ‘which face’ corresponded with how their pain felt. Thus the ‘scaleness’ of the Facial Affective measure in terms of its visual presentation was diminished, perhaps reducing the impact for cognitive developmental differences which are partly responsible for age effects in scale application by children. There is little known on how different scale formats and methods influence children’s descriptions and estimates of their pain. Future studies could perhaps compare randomized Faces Pain and the Facial Affective Scales, and examine the relative strengths of the correlations under conditions where the scales values are systematically randomized or ordered in their presentation format. A second aim of the study was to examine how ratings on the four pain measures were predicted by the same set of variables, after the influence of age had been controlled for. The variables of interest (see Table 5) comprised information about a child that can be recorded prior to blood sampling and that could be sensibly estimated by a companion parent. The variable set did not include measures of preprocedural anxiety or expectations for pain obtained directly from the child (due to institutional ethical considerations; see Materials and Method). These predicted pain and anxiety estimates are known to account for large portions of the variance in self-reported pain ratings (e.g. Goodenough et al., 1997), and the finding that, generally, little more than 30% of the variance could be accounted for without the inclusion of these variables was not surprising (Table 5). Overall, the results indicated minimal effects for individual variables. The exceptions seemed to be a small impact of needle history estimates, indicating some influence of the time

PA/N

313

lapse since last needle on the scores for the affective measures, and the estimate of the total number of needles for the intensity measures. Secondly, for the MVAS-intensity ratings, higher scores were predicted by the child having watched a family member receive a needle some time prior to the current blood test (Step 8, Table 5). It is not immediately clear why proportionally more variance was able to be explained for the MVAS-intensity measure (48%) as compared with the other three measures (Table 5). If it were the product simply of the age appropriateness of the analogue concept, then a similarly large effect of age would have also been expected on the MVAS-unpleasantness ratings, but this was not the case. One possibility concerns the fact that the four measures were administered in a lixed order to help children understand how to use the scales and the concepts to be measured. In this fixed order, MVAS intensity preceded the MVAS unpleasantness. There may have been a type of practice carry-over effect in the use of the mechanical visual analogue scale which affected the MVAS-unpleasantness scores, whereby younger children had grasped a better idea on how to manipulate the scale more precisely on the second time they were asked to move the central slider. This would suggest, however, that the MVAS-intensity ratings for younger children were likely to represent overestimates of pain, especially for the 4-year-olds in the sample (see Fig. 3). A cross-check of the proportions of variance accounted for by age with the 4-year-olds omitted from the analysis served to reduce the absolute proportions of variance for each measure, but the proportional disparity between the MVAS-intensity and the other three measures persisted in the same ratio of approximately 2:l (change in Y* for entry of age after controlling for needle type was: 5% for the Faces Pain Scale; 2% for the Facial Affective Scale; 6% for the MVASunpleasantness; and 10% for the MVAS-intensity). Therefore, a predominantly age-focused account does not appear to wholly explain the results for MVAS-intensity. Overall, the results of these regression analyses indicate that pain experience and pain report reflect a package of many different factors European

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related to the child, the child’s family, and the pain event itself. Large scale studies will be needed in order to determine whether some of the smaller effects identified here (e.g. time since last needle) are meaningful, and whether there is any likelihood that estimates of prior needle experience could actually account for more of the variance in pain ratings if children (especially those younger than 6 years of age)could reliably provide the needle history data: to date, both clinicians and researchers necessarily rely on parental corroboration for quantitative estimates (e.g. time since last needle), and on the assumption that young children are invariably accompanied by an adult for health-related visits. There is also some hint from the relative sizes of the partial regression coefficients for an influence of anatomical metrics (surface area, body mass). Previously, it had been found that an estimate of body surfacearea could predict pain ratings after chronological age had been controlled for (Goodenough et al., 1997). A formal replication of this finding was precluded by the fact that the children in the present study were sampled from a much more restricted age range than the 3-15 years sample of the original paper. In conclusion, the present research indicates that the FacesPain Scaleand the Facial Affective Scale provide measures of intensity and affect which appear to be more distinctive than a pair of similar estimates of these constructs derived from the visual analogue paradigm. Thus, facial expression scales would appear to be the most age-appropriate choice in currently available measures for helping children of a wide age range to separately estimate these two dimensions of pain. In this sense,future researchcould also examine the application of a ‘paired face scale’ paradigm for obtaining self-report pain estimates from the adult cognitively impaired and elderly populations-a group who have already shown some benefit in using paediatritally oriented measures such as the Faces Pain Scale (e.g. Herr et al., 1998). It remains to be determined, however, to what extent differences in ratings derived from thesetwo facial scalesare clinically meaningful in terms of their utility in determining treatment options, especially as only the Facial Affective Scale is a bipolar measure. European

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3

ET AL.

ACKNOWLEDGMENT We would like to thank the nursing staff of Prince of Wales Hospital Pathology and Sydney Children’s Hospital Haematology Clinic for their generousassistanceand co-operation. We would also like to thank Christine Chambers for reviewing an earlier draft of this manuscript. This study was presented at the 20th Annual Scientific Meeting of the Australian Pain Society (April 1999,Fremantle). The researchwas partially supported by the Big Brother Movement, the Andrew Thyne Reid Charitable Trust, and a National Health and Medical ResearchCouncil Grant (p/n 970858) awarded to authors BG and GDC. We also gratefully acknowledge generous private donations from the Franciscan Friars (Waverley, Sydney) and Mrs Mary McKell (Double Bay, Sydney). REFERENCES Arts SE, Abu-Saad HH, Champion GD, Crawford MR, Fisher RJ, Juniper KH and Ziegler JB. Age-related response to lidocaine-prilocaine (EMLA) emulsion and effect of music distraction on the pain of intravenous cannulation. Pediatrics 1994; 93: 797-801. Bieri D, Reeve R, Champion GD, Addicoat L, Ziegler JB. The Faces Pain Scale for the self-assessment of the severity of pain experienced by children: development, initial validation, and preliminary investigation for ratio scale properties. Pain 1990; 41: 139-150. Chambers CT, Craig KD. An intrusive impact of anchors in children’s faces pain scales. Pain 1998; 78: 27-37. Champion GD, Goodenough B, von Baeyer CL, Thomas W. Measurement of pain by self-report. In: PJ McGrath, GA Finley, editors. Measurement of Pain in Infants and Children. Seattle: IASP Press; 1998. Fowler-Kerry S, Lander JR. Management of injection pain in children. Pain 1987; 30: 1699175. Fowler-Kerry S, Lander J. Assessment of sex differences in children’s and adolescents’ self-reported pain from venipuncture. J Pediatr Psycho1 1991; 16: 783-793. Fradet C, McGrath PJ, Kay J, Adams S, Luke B. A prospective survey of reactions to blood tests by children and adolescents. Pain 1990; 40: 53360. Goodenough B, Kampel L, Champion GD, Nicholas MK, Laubreaux L, Ziegler JB, McInerney M. An investigation of the placebo effect and other factors in the report of pain severity during venipuncture in children. Pain 1997;72:383-391. Goodenough B, Champion GD, Laubreaux L, Tabah L, Kampel L. Needle pain severity in children: does the relationship between self-report and observed behaviour vary as a function of age? Austr J Psycho/ 1998; 50: 1-9.

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Hotelling H. The selection of variates for use in prediction, with some comments on the general problem of nuisance parameters. Ann Math Stat 1940; 11: 271-283. Lander J, Fowler-Kerry S. Age differences in children’s pain. Perceptual Motor Skills 1991; 73: 415418.

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