An Evaluation of the Faces Pain Scale with Young Children

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1 122 Journal of Pain and Symptom Management Vol. 20 No. 2 August 2000 Original Article An Evaluation of the Faces Pain Scale with Young Children Mick Hunter, PhD, Lee McDowell, MSc, Ruth Hennessy, MSc, and John Cassey, MB BS, FRACS Department of Psychology (M.H., L.M., R.H.), University of Newcastle, Callaghan; and Department of Pediatrics (J.C.), John Hunter Hospital, New Lambton, New South Wales, Australia Abstract The psychometric characteristics of the Faces Pain Scale (FPS) were evaluated in three groups of preschool and school-aged children ( ; and years, respectively). The FPS was adequately comprehended by even young children. It was easily administered and was valid and discriminating. It did not, however, possess the linear scalability claimed by its authors. J Pain Symptom Manage 2000;20: U.S. Cancer Pain Relief Committee, Key Words Pain perception, pediatrics, Faces Pain Scale, psychometrics Introduction In 1984, Ross and Ross claimed that, in spite of the burgeoning experimental interest in pain in adults, the measurement and evaluation of pain in...infants, children and young adolescents has been almost completely ignored. 1 Some developments must have been made during the intervening period, since a more recent article claimed that... the past 20 years have brought realization to the clinicians involved in the treatment of children that pain is a real phenomenon in children. 2 However, some central issues of pediatric pain and its evaluation still persist. For example, the accurate measurement of pain remains a particular problem with younger children, who possess poorer and less well-developed linguistic skills. Eliciting a Send reprint requests to: Mick Hunter, PhD, Department of Psychology, University of Newcastle, Callaghan, New South Wales, 2308, Australia. Accepted for publication: September 15, child s conceptual appreciation of pain is also problematic. Pain can be an abstract concept, but it is also a personal experience that carries strong emotional and motivational connotations. The experience can be variable both within and between individuals, can be used to refer to distress as well as physical pain, and is highly context sensitive. The concept itself has a chameleon-like tendency to alter and be hard to pin down. 3 Nonetheless, the accurate measurement of pain in children is essential for monitoring treatment, especially when aggressive treatment of pain is recommended. 2 A large number of measurement techniques have been devised to measure pain in children. These include observational checklists, physiological responses, self-report questionnaires, selections from lists of descriptors, selection from interval scales (such as face-scales and pain thermometers), visual analogue scales (VAS), and projective techniques (for reviews of these, see the references 4 6). The psychological measures are all based on either domain sampling or psychophysical scaling. 7 Do- U.S. Cancer Pain Relief Committee, /00/$ see front matter Published by Elsevier, New York, New York PII S (00)

2 Vol. 20 No. 2 August 2000 The Faces Pain Scale and Young Children 123 main sampling approaches (e.g., descriptor selection) provide useful qualitative information, with some quantitative data, but yield only categorical measures. Psychophysical scaling techniques, such as VAS, provide quantitative data, but do not give the same richness of qualitative information. Whereas VAS techniques provide ordinal scaling, they are unlikely to provide interval scale measures unless a subject is capable of linearly scaling his or her own sensations a somewhat unlikely ability. In addition to these difficulties, age has an important effect on children s responses to pain measures. While some studies, most notably the early studies of Savedra et al. 8 and of Ross and Ross 1,9 found no clear age or gender effects, later investigators have suggested that children s responses vary with age level. Gaffney and Dunne, 10 in a large sample of 5 14-year-olds, found differences in pain descriptions, which they suggest show a developmental pattern commensurate with Piagetian notions of concept formation and development. Harbeck and Peterson 11 also found age differences between five age groups of subjects stretching from 3 4-year-olds to college freshmen. They suggest that these differences...parallel other aspects of cognitive development. It would seem that a pain scale for children is likely to be compromised unless the problems of scalability and age sensitivity can be overcome. Among the scales that have been developed, the appeal and popularity of face-scales, such as the Oucher Scale, 12 the Smiley Five Face Scale, 13 the Affective Facial Scale, 14 and the Faces Pain Scale (FPS), 15 is understandable. These scales comprise pictures of faces depicting expressions showing various levels of a pain response. They are generally appealing to children and they are popular with clinical staff, as they are relatively quick and easy to administer. Unfortunately, there are conceptual and psychometric difficulties with these scales. For example, there are difficulties distinguishing acute pain from distress and anxiety. There are also problems in establishing the degree to which the faces in a scale can be said to form a genuine continuum. 16 Nevertheless, the careful development and testing of the FPS 15 led the authors of this scale to claim that it is not only a valid and reliable scale, but also that it can be regarded as an interval scale and that it is appropriate for younger age groups of children. In their study, Bieri et al. 15 tested a large sample of school children in two age groups, 6 7-year-olds and 8 9-year-olds. Their results indicate that the scale is discriminating, but they also indicate that age level affects the response, with younger children being more variable in their accuracy. The aim of the present study was to extend the work of Bieri et al. by further investigating the psychometric characteristics of the FPS. We tested the responses to the FPS of younger age groups of children by testing a sample of kindergarten and school children aged from 3 1/2 to 6 1/2 years. Method Subjects A total of 135 normal healthy girls and boys were the subjects in this experiment. They ranged in age from three-and-a-half years to sixand-a-half years and were recruited from kindergartens and primary schools in the city of Newcastle, New South Wales, Australia. The 69 girls and 66 boys were grouped according to age into three groups; Group 1 (n 45, 22 girls and 23 boys) aged between 3 years 6 months and 4 years 6 months (mean 4.2 years); Group 2 (n 45, 26 girls and 19 boys) aged between 4 years 6 months and 5 years 6 months (mean 4.9 years) and Group 3 (n 45, 25 girls and 20 boys) aged between 5 years 6 months and 6 years 6 months (mean 6.2 years). Group size was determined by power calculations based on the data of Bieri et al. 15 Their data for the proportions of correct ordered placement of pairs of faces indicate that a group size of 45 yields a power of 0.8 for an level of Instruments The FPS was administered to the children in various ways. The FPS comprises 7 cards depicting schematic faces conveying increasing levels of pain intensity, from no pain (Face 1) to severe and excruciating pain (Face 7) (see Figure 1). Each face is represented by a line drawing on cards measuring 8 cm by 10 cm. The face is 6 cm from top to bottom. In addition, building blocks were used in part of the experiment. Procedure Following ethical approval, permission to recruit subjects was sought from kindergartens, schools, principals, staff, parents, and guardians.

3 124 Hunter et al. Vol. 20 No. 2 August 2000 Fig. 1. The Faces of FPS from Face 1 (no pain) on the left to Face 7 (extreme pain) on the right. All testing was performed individually with the child sitting comfortably at a desk opposite the experimenter. A few minutes were spent before testing in order to establish rapport with the child and to obtain some notion of the child s understanding of the concept of pain. In the youngest children the notion of hurt was familiar even though the concept of pain sometimes was not. Once the experimenter had deciphered the child s preferred pain language and was satisfied that the child understood the notion of pain then testing began. Throughout testing the child s own pain language was used. The FPS was presented in four different ways. Firstly, Phase 1, all 7 cards were laid out randomly on the desk and the child was asked to place the faces in order of pain expression from least pain to most pain. Secondly, Phase 2, the child was shown all possible pairs of cards, one pair at a time and asked to say which of any pair expressed more pain. The pairs were ordered randomly. Thirdly, Phase 3, a pile of 12 wooden toy building blocks was given to the child and the experimenter said that the blocks represented pain. The experimenter then placed the Face 1 (no pain) in front of the child and explained that the first face card got no blocks because it showed no pain. Then the experimenter placed Face 7 in front of the child and piled up 6 blocks explaining that 6 blocks represented the worst pain possible. These two examples were left in front of the child and the remaining 5 face cards were presented in random order with the child being asked to decide how many blocks were needed to represent the amount of pain depicted on the face. The children then built a tower with that number of blocks and placed it in front of the card. Thirty children in each age group completed Phases 1 to 3 of the experiment. The groups were balanced for gender. Fifteen additional subjects in each age group, again balanced for gender, completed the fourth presentation, Phase 4. Phase 4 was a testretest reliability check in which children were shown all 7 face cards and asked to choose a card to reflect the amount of pain they thought appropriate to each of nine different painful experiences. The painful experiences were: falling over and sustaining a skin abrasion; having an injection or needle puncture; burning their fingers (say on a cooking pot); having a bandage pulled off their skin; trapping a finger in a door; sustaining a bee sting; having their hair pulled; and being pinched. All were chosen for their likelihood of having been experienced by the children. Whether or not the child had experienced an event was also recorded. At retest one week later, the children were given exactly the same task again. Results Phase 1: Placing Faces in Order of Perceived Pain After initial screening of the results for all 90 children who completed Phase 1, the number of correct and incorrect responses were interpolated as a percent correct response for each Face in the series and plotted by age group. As can be seen in Figure 2, the extremes of the faces continuum (Faces 1 and 7) were placed with almost complete accuracy by all age groups. More difficulty was experienced by the children positioning Faces 3, 4, and 5. These categorical data, the rank orders of Faces produced by the different age groups of children, were subjected to a Kruskall-Wallis significance test. No statistically significant differences were found between the rank orders of the three age groups, although a comparison of the performance of Group 2 with the other two groups approached significance ( ; P 0.068). In order to identify which Faces were most difficult for the children to rank, the obtained rank orders were compared with the correct order. For each child s rank, the number of ranks distant of each Face from its correct ranking was calculated. Table 1 shows the mean rank positions distant from its correct position of each Face card in the series by Group.

4 Vol. 20 No. 2 August 2000 The Faces Pain Scale and Young Children 125 was significantly worse than the girls ( ; P 0.04). Other than this, the trend of the errors showed that girls made the greatest positional error on Face 5 and the boys on Face 6. In order to assess the concordance of the rank orders provided by the children the data were also analyzed using Kendall s Coefficient (W). The obtained W can be transformed into a significance test by the formula: 2 (n 1) m(n 1)W, where m is the number of items in the scale. Table 2 shows Kendall s W and the associated 2 values for the sample overall, and by age group and gender. All comparisons show high levels of concordance indicating high levels of agreement in the rank orders provided. Fig. 2. The accuracy of ordering of Faces shown by Group 1 (youngest children: years: solid line); Group 2 ( years: dotted line) and Group 3 (oldest children: years: dashed line). Table 1 shows that the youngest children (Group 1) placed Face 5 at the greatest distance from its correct rank order; Group 2 ( years old) placed Face 5 at the greatest distance; and the older children in Group 3 placed Face 6 at the greatest distance. Chi square comparisons of the data for Face 5 yielded a significant difference in the ability of the children to correctly position Face 5, with the Group 2 children performing more poorly than the other groups ( ; P 0.02). The Table also shows the generally good performance and sharp focus of the youngest children, with only Faces 3, 4, and 5 causing any confusion, whereas Group 2 made larger errors of judgement over a greater number of Faces, and Group 3, while making fewer errors, did so over Faces 2, 3, 4, 5, and 6. There was one statistically significant difference between the performance overall of girls and boys. The boys positional error for Face 6 Table 1 Mean Number of Nominated Rank Positions Deviating from the Correct Rank Position (Phase 1) of each Face Card by Group Faces Age groups Phase 2: Rank Ordering on the Basis of Paired Comparisons Table 3 shows the percentage of errors made by the children when requested to nominate the Face with the most pain between randomly chosen pairs of faces. Since these scores represent an interval scale they were subjected to an analysis of variance (ANOVA) in a Group (age groups 1, 2, and 3) by Gender (girls and boys) design. There was a significant main effect for Group (F(2, 87) 9.90; P 0.05) with the youngest children (Group 1) making a higher percentage of errors than the other two groups. There was neither a significant main effect for Gender nor a significant Group by Gender interaction. Phase 3: Equivalence of Pain Estimate in Another Modality The number of building blocks allocated by the children to Faces 2 6 which were either Table 2 Kendall s Coefficient of Concordance (W) for Ordering of Faces (Phase 1) Subjects W 2 df Group 1 (n 30) Group 2 (n 30) Group 3 (n 30) All groups combined (n 90) All males (n 41) All females (n 49)

5 126 Hunter et al. Vol. 20 No. 2 August 2000 Table 3 Percentage of Incorrect Judgments in Paired Comparisons (Phase 2) for all Possible Pairs of Face Cards Group Faces 1 Faces Table 4 Mean Number of Allocated Blocks Deviating from the Implied Correct Number (Phase 3) Faces Group All Males All Females over or under estimates expected from a linear scale (i.e., 1 block for Face 2; 2 blocks for Face 3, etc.) were the measure in this presentation. Table 4 shows the mean number of blocks over or under estimated for each Face card by Group. These data consist of absolute numbers of blocks, nevertheless they do not represent a true interval scale since the task given to the children requires them to estimate, in terms of building blocks, the pain on each separate Face. The boundaries of the scale are set by the experimenter but the linearity of the scale is left implicit and it is the children s task to estimate as they think fit. The objective of this task is as much to see if the children recognize the implicit linearity of the scale as it is to determine their estimates of each Face. The degree of over or under estimation represents a deviation from an implicit linear series. Because of the nature of these data, they were subjected to a Kruskall-Wallis test. The significance test revealed a main effect for age ( ; P 0.001) with the youngest children deviating more than the other groups from a linear series. There was no main effect for Gender ( ; P 0.82). The fact that the youngest children deviated more from the linear series in their estimates suggests that either they were less capable of estimating with numbers of blocks or they were less capable of appreciating the implicit linear nature of the series. Either way it justifies caution in interpreting the Faces Scale as a linear scale, at least for very young children. The youngest children performed well on the Phase 1 task but less well on the Phase 2 and 3 tasks. Phase 4: Test-Retest Reliability The children who took part in the test-retest reliability study did not take part in the other phases of the experiment. Spearman s rank order correlation was used to assess the degree of agreement between the Face cards ascribed to the different painful experiences on two separate occasions. Some of the children had not experienced all of the pain situations presented. For those situations they were asked to imagine what the pain would be like. The imagined pain experience measures showed much greater variability and lower correlations than the situations that had been experienced and so these data are not reported here. Table 5 shows the correlation coefficient and the sample size of the test-retest measures for the children who had experienced the pain situations. As might be anticipated, the older age group reported experiencing more painful events. Moreover, there was a large variability in the number of children experiencing the different events. The correlations range from (mean 0.56) for Group 1; from (mean 0.58) for Group 2 and from (mean 0.57) for Group 3. Overall combined correlations ranged from (mean 0.55). These results suggest only moderate test-retest reliability even after only a short period of time and they raise questions concerning the scale s reliability over the longer term. However, the small sample size used in Phase 4 must be kept in mind when considering these data.

6 Vol. 20 No. 2 August 2000 The Faces Pain Scale and Young Children 127 Table 5 Test-Retest Correlations of Pain Events Experienced (Phase 4) Fall Needle Burn Bandage Hand in Door Bee Sting Hair Pull Pinch Tickle All Subjects r n (n 39) (n 35) (n 14) (n 40) (n 26) (n 14) (n 35) (n 38) (n 43) P Age Group 1 r not computed n (n 13) (n 8) (n 4) (n 15) (n 9) (n 5) (n 13) (n 15) P Group 2 r n (n 12) (n 13) (n 4) (n 12) (n 7) (n 6) (n 10) (n 13) (n 14) P Group 3 r n (n 14) (n 14) (n 6) (n 13) (n 10) (n 3) (n 12) (n 10) (n 14) P Males r n (n 23) (n 21) (n 5) (n 24) (n 15) (n 7) (n 18) (n 21) (n 23) P Females r n (n 16) (n 14) (n 9) (n 16) (n 11) (n 7) (n 17) (n 17) (n 20) P In summary, this psychometric study indicates that the Faces pain scale, while not defensible as a linear scale, is nonetheless a scale that even the very young can understand and use appropriately, and one with which children are able to discriminate levels of pain in a consistent fashion. Question marks still remain over the discriminability of Faces 5 and 6, over the accuracy of the estimates of very young children, and over the test-retest reliability of the scale. Discussion In this experiment, we attempted to explore the psychometric characteristics of the FPS and to evaluate the scale s usefulness with young children. A number of issues are raised by the results. Firstly, the scale s aims and intentions appeared to be understood by the even the youngest of our groups of children. This, combined with the ease of administration of the test, make it appealing as a clinical instrument. The provision of a clear explanation of the test requirements and the importance of gaining an appreciation of the pain language of the child have been emphasized by others 11 and were key elements in our procedure. These elements should not be overlooked in any general clinical implementation of the FPS. The FPS was found to be sensitive and discriminating in this study. No outliers were found in the initial screening of the data, suggesting that all the children were capable of making meaningful discriminations. However, the difficulties encountered by the children with Faces 3, 4, and 5 in Phase 1 of testing and the errors elicited in Phase 2 with Faces 5 and 6 suggest that, while the Faces form an acceptable series, they do not qualify as an interval scale. It is possible that some amendments to the scale could improve its psychometric profile. The removal of Face 5 with some minor adjustments to Face 4, for example, could help to reduce confusion in the middle of the scale. Any such changes would require further psychometric evaluation. While gender differences in response to pain have been noted by some investigators, 13,17 the results here suggest that there are few significant differences between girls and boys in their interpretations of the facial expressions of pain represented on the face cards. We recorded one significant difference the error scores for positioning Face 6 in Phase 1 of testing were greater for boys than girls. This difference may indicate that the boys were less accurate, or less concerned with accuracy, than were the girls. However, this seems

7 128 Hunter et al. Vol. 20 No. 2 August 2000 unlikely since no other gender differences were recorded in any of the other positioning error scores, nor indeed, in the overall ranking or the randomized paired comparisons of Faces. Moreover, Face 6 was not one of the Faces that caused most confusion in the ranking exercises. Without further experimental evidence we cannot offer an explanation for this seemingly anomalous result. Our results also support the notion proposed by Gaffney and Dunne, 10 McGrath, 4 and by Harbeck and Peterson 11 that developmental maturity affects the child s capacity to estimate pain. In general, age-related effects followed a predictable pattern with overall accuracy being poorest for the youngest children, although in Phase 1, it was Group 2 which was the least accurate. This latter finding is somewhat at odds with the Piagetian interpretation of pain perception proposed by Gaffney and Dunne, 10 since such an interpretation predicts a strictly progressive developmental pattern paralleling the stages of cognitive development. Other recent work by Hayes and Haslam 18 has also challenged the Piagetian view. Hayes and Haslam compared children s estimates of pain resulting from both external and internal causes and noted that, contrary to the Piagetian view, preschool children rated internal pain as more painful than did 11-year-olds, regardless of individual pain experience. It would seem that the relationship between cognitive development and pain perception is more complicated than that envisaged by Gaffney and Dunne. The final issue concerns the attempt to measure the test-retest reliability of the FPS. This attempt was not successful. The large degree of variability in the responses of the children when they were asked to imagine what pain would be involved in a particular painful event suggested that these data were unreliable. When we then reduced the data set to include only the responses of children who had experienced the event, the resulting sample sizes were much smaller than initially envisaged. The test-retest reliability of the FPS requires a better demonstration than is offered here. Nevertheless, it is worth noting that evaluations of similar scales have also yielded poor reliability measures. 19 In summary, the FPS seems to offer a simple and useful tool for estimating pain in children. However, the responses of the children in our study suggests that the scale is best reserved for at least school-aged children. Acknowledgments We would like to express our gratitude to the Department of Psychology, University of Newcastle for its financial support for this project; and to the schools, preschools, and children who participated in the study. References 1. Ross DM, Ross SA. The importance of type of question, psychological climate and subject set in interviewing children about pain. Pain 1984;19: Bhatt-Mehta V. Current guidelines for the treatment of acute pain in children. Drugs 1996;51: Varni JW, Waldron SA, Gragg RA, Rapoff MA, Bernstein BH, et al. Development of the Waldron/ Varni pediatric pain coping inventory. Pain 1996;67: McGrath PA. An assessment of children s pain: a review of behavioral, physiological and direct scaling techniques. Pain 1987;31: McGrath PA. Pain in Children: Nature, Assessment and Treatment. New York: Guildford Press, Turk DC, Melzack R. Handbook of Pain Assessment. New York: Guildford Press, Doctor JN, Slater MA, Atkinson JH. The descriptor differential scale of pain intensity: an evaluation of item and scale properties. Pain 1995;61: Savedra M, Gibbons P, Tesler M, Ward J, Wegner C. How do children describe pain? A tentative assessment. Pain 1982;14: Ross DM, Ross SA. Childhood pain: the schoolaged child s viewpoint. Pain 1984;20: Gaffney A, Dunne EA. Developmental aspects of children s definitions of pain. Pain 1986;26: Harbeck C, Peterson L. Elephants dancing in my head: a developmental approach to children s concepts of specific pains. Child Dev 1992;63: Beyer JE, Aradine CR. Content validity of an instrument to measure young children s perceptions of the intensity of their pain. J Pediatr Nurs 1986;1: Jylli L, Olsson GL. Procedural pain in a paediatric surgical emergency unit. Acta Paediatr 1995;84: McGrath PA, DeVeber LL, Hearn MT. Multidimensional pain assessment in children. In: Fields HL, Dubner R, Cervero F, eds. Advances in Pain

8 Vol. 20 No. 2 August 2000 The Faces Pain Scale and Young Children 129 Research and Therapy, 9. New York: Raven Press, 1985: Bieri D, Reeve RA, Champion GD, Addicoat L, Ziegler JB. The Faces Pain Scale for the self-assessment of the severity of pain experienced by children, initial validation and preliminary investigation for ratio scale properties. Pain 1990;41: Kuttner L, LePage T. Faces scales for the assessment of pediatric pain: a critical review. Canadian J Behavioral Science 1989;21: Schechter NL, Bernstein BA, Beck A, Hart L, Scherzer L. Individual differences in children s responses to pain: role of temperament and parental characteristics. Pediatrics 1991;87: Hayes BK, Haslam SA. Developmental changes in the understanding of pain: a challenge to the Piagetian account. (Personal communication, 1995). 19. Belter RW, McIntosh JA, Finch AJ, Saylor CF. Preschoolers ability to differentiate levels of pain: relative efficacy of three self-report measures. J Clin Child Psychol 1988;17: