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

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 (r = 0.77) 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 (r = 0.64) than for intensity (r = 0.51). 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. (C) 1999 European Federation of Chapters of the International Association for the Study of Pain.