Abstract
This study describes the comparison of multiple and single pain ratings in patients after surgical removal of the third molar. Correlation and agreement analysis were performed between the average pain intensity measured three times a day over a period of 7 days and one single pain rating (designated the ‘recalled average’ pain, as assessed by the patient) after surgical removal of the lower third molar. The study population consisted of patients participating in three randomized trials. The results show that both measurement correlated good to excellent, but there was a large variation in agreement between the ratings. In conclusion, in patients with surgical third molar removal a single pain rating is not an accurate predictor of the average pain measured by a multiple pain-rating test. A single pain rating cannot replace a multiple pain assessment.
Impaction of the third molar is a common disorder, which often necessitates tooth removal. The postoperative period after surgical removal of mandibular third molars is frequently characterized by swelling, pain and temporary restricted mouth opening. In studies concerning removal of the third molar, pain assessment is a crucial measurement. In most of these studies a multiple pain rating is used as the primary pain outcome.
In the assessment of pain, pain reports tend to change over time, even during the course of a day. Jensen et al. have shown that in patients with chronic pain a single pain intensity rating was the least reliable, whereas three pain intensity measurements a day over the course of 4 days showed excellent internal consistency and validity.
Multiple assessments are impractical both in the clinical and research setting, therefore Dworkin and Siegfried suggested that patients may be able to assess their own average pain levels over a period of time simply by asking them to rate their pain ‘on average’ at a single point in time. For patients with chronic pain a single rating of pain ‘on average’ is an accurate estimate of ‘actual average’ pain intensity measured over the course of 7 days. In contrast, Beese and Morley demonstrated that memory for acute pain experience is inaccurate.
There are different methods to compare clinical measurements. A frequently used method is the Bland–Altman agreement analysis. According to Bland and Altman, such a comparison should be based on the differences between the two measurements performed on the same subject. The mean differences would be the estimated bias – the systematic difference between measurements. Further, the standard deviation (SD) of the differences would measure random fluctuations around this mean. In addition, the 95% limits of agreement (mean differences plus or minus 1.96 standard deviations (SDs)) can be used to determine how far apart measurements by the two assessments are likely to be for most people.
The present study was designed to investigate whether a single pain rating in patients with surgical third molar removal can replace a multiple pain-rating test. For this purpose, the authors performed correlation and agreement analyses according to Bland and Altman between the average pain intensity measured three times a day over the course of 7 days and one single pain measurement of pain ‘on average’ in 220 patients.
Material and methods
The data for this study consisted of the pain intensity assessments measured in 220 patients who participated in three different trials concerning surgical removal of the third molars. The results of one of these trials are described elsewhere. The results of the other two trials are in preparation. The patient characteristics of the trials are given in Table 1 .
| Trial I | Trial II | Trail III | |
|---|---|---|---|
| Patients | 95 | 63 | 62 |
| Age (mean ± SD) | 26.78 ± 9.54 | 30.01 ± 7.92 | 24.91 ± 5.42 |
| Sex | |||
| Male | 47 | 25 | 25 |
| Female | 48 | 38 | 37 |
All patients in the trials were asked to rate their pain, three times a day over the course of 7 days, on a 100 mm visual analogue scale (VAS), which was anchored by two extremes of pain: ‘no pain’ on the left and ‘the worst possible pain’ on the right end. At the end of the 7 days they were asked to note their average pain for the week using a VAS with the same extremes.
Statistics
The pain intensity measured with the single VAS is referred to as ‘recalled average’ pain, whereas the calculated average pain intensity noted over 7 days is the ‘actual average’ pain. For comparison of these two entities, the intraclass correlation coefficient (ICC) was used.
This coefficient was defined as follows: 0.5–0.6 moderate; 0.6–0.8 good; and 0.8–0.10 excellent. To assess the agreement between the two measurements the authors compared the difference of these two pain measurements for each patient with the average of both measurements for each trial, as described by Bland and Altman. The limit of agreement (LOA) is defined as the mean differences of two measurements plus or minus 1.96 times the SD of the mean differences ( M ± 1.96 SD). For the Bland and Altman analyses the pain measures were natural log transformed due to the skewed distributions. Subsequently data were back-transformed (antilog) to make interpretation possible on the original scale. According to the literature a clinical relevant pain reduction, measured on a VAS, varied between 14 and 18 mm. A study by Martin et al. (manuscript currently under review) indicated that an absolute pain reduction of 20 mm on the VAS, was of clinical relevance, after surgical removal of third molars. The authors also evaluated the agreement using LOAs at 20 mm difference in VAS scores.
Statistics
The pain intensity measured with the single VAS is referred to as ‘recalled average’ pain, whereas the calculated average pain intensity noted over 7 days is the ‘actual average’ pain. For comparison of these two entities, the intraclass correlation coefficient (ICC) was used.
This coefficient was defined as follows: 0.5–0.6 moderate; 0.6–0.8 good; and 0.8–0.10 excellent. To assess the agreement between the two measurements the authors compared the difference of these two pain measurements for each patient with the average of both measurements for each trial, as described by Bland and Altman. The limit of agreement (LOA) is defined as the mean differences of two measurements plus or minus 1.96 times the SD of the mean differences ( M ± 1.96 SD). For the Bland and Altman analyses the pain measures were natural log transformed due to the skewed distributions. Subsequently data were back-transformed (antilog) to make interpretation possible on the original scale. According to the literature a clinical relevant pain reduction, measured on a VAS, varied between 14 and 18 mm. A study by Martin et al. (manuscript currently under review) indicated that an absolute pain reduction of 20 mm on the VAS, was of clinical relevance, after surgical removal of third molars. The authors also evaluated the agreement using LOAs at 20 mm difference in VAS scores.
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