Comparison of internal reliability and validity of the McGill Pain Questionnaire and the Short Pain Inventory

Abstract

We compared the psychometric properties of the McGill Pain Questionnaire (MPQ) with the 17-item Short Pain Inventory© (SPI) in 60 outpatients with osteoarthritic knee pain. Split-half reliability, Guttman split-half reliability, Cronbach alpha and the correlation between the first and second half of the test were higher in the SPI total pain disturbance than any of the summary or subscales of the MPQ: 0.94, 0.94. 0.88 and 0.90, versus 0.71, 0.70, 0.69 and 0.55 for the MPQ sensory present pain intensity, 0.59, 0.57, 0.65 and 0.43 for the affective and 0.62, 0.55, 0.49 and 0.45 for the evaluative MPQ scale, respectively. The parameters for the SPI total mood disturbance were superior to all MPQ-derived scales. Dividing into high and low ‘pain experienced right now’ identified screening samples. The SPI ‘pain right now’ was more discriminating than the comparative MPQ item on both the SPI and MPQ. Additionally, none of the summary scales of the MPQ could show significant internal discrimination whereas the SPI did achieve this. There were 23 significant correlations with the SPI severity compared with 15 with the MPQ. SPI sadness, anxiety, anger, total mood disturbance and total pain disturbance were significantly correlated with the MPQ severity rating. The MPQ variables fared less well than the SPI in the degree of association between various pain parameters and physical severity. Factor analyses revealed that the SPI accounts for the majority of the variance (50%) compared with 17% for Factor 2. This second factor is best indexed by the McGill ‘pain now’ and also with the SPI ‘pain severity now’ item. Since the SPI indexes the severity as accurately (0.79) as the McGill, the only difference between the two is the sensory MPQ variance. However, since the SPI (Factor 1) also indexes some of the common variance of the MPQ sensory variable, the SPI also gains in this respect. If it were the case that the outcome of an analgesic clinical trial was the sensory aspects of the pain (cutting, throbbing, rasping) then the McGill should be the obvious outcome measure. For the patient, the most important feature of pain surely must be the physical severity and the unpleasantness of the experience. The MPQ is a rather long procedure and the evaluative scale is of dubious value. The majority of the pain variance is captured by the SPI and, secondly, by the sensory aspect of the MPQ. The SPI measures the emotional aspects of pain well and the McGill assesses the physical or sensory aspects of pain better than any other available. Both have their place according to one’s research interests and the clinical relevance. For example, if an investigation involves opiates like morphine, the SPI may be the better placed instrument, since the induced euphoria may present as a patient who can still feel the pain but is no longer bothered by it. Algesimetry requires measuring both the physical and emotional sensations of the patient.