Discussion
Pain, chronic musculoskeletal pain, pain, chronic pain, NRS
CHRONIC PAIN, MINOR
We compared two different anchors for the extreme high pain score for an NRS. Scores using the anchor “extremely severe pain” had stronger associations with known correlates of pain than when using the anchor “worst pain imaginable” without changing average pain scores. This relationship was unaffected by self-reported creativity. Although there has been considerable research on different pain scales - VAS, verbal rating scales, and NRS – there has been little work related to the differing anchor texts. In reviewing currently available pain outcomes measures, the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) found that different methods to all be reliable and valid, but no scale was consistently better [We did find one study, by Seymour et al., which explicitly compared different anchor texts (referred to as “end-phrase” throughout their paper) on VAS. Limited to 100 patients with dental pain, Seymour et al. compared the following four anchor texts: “troublesome”, “miserable”, “intense”, and “unbearable” to “worst pain imaginable” and saw that as the anchor became more extreme, the more the histogram would shift towards lower scores. Considering the shape of the histogram, combined with prompting the fewest observations at the extremes, they concluded that the text “worst pain imaginable” was the most suitable anchor. There were 14 responses at the extreme for the anchor of “worst pain imaginable” compared to the next lowest value of 18 (anchor text “troublesome”) for the question asking about present pain, and 6 compared to the frequency of 11 (anchor text “intense” and “unbearable”) when asking about worst pain [Another common area of focus regards potential cutoffs to define severe pain. Boonstra et al. reported the cutoffs of ≤ 5 for mild, 6–7 for moderate, and ≥ 8 for severe pain in patients with chronic musculoskeletal pain [The participants in our study coincide with what would be expected for chronic pain patients. Breivik and colleagues conducted a cross-sectional telephone survey of nearly 9,000 people in 15 European countries and Israel and estimates the prevalence of chronic pain (≥ 6 months) in adults to be approximately 19%. Among those with chronic pain, respondents reported their pain intensity when they last experienced pain ≥ 5. In further interviews with nearly 5,000 people with chronic pain, the average age was 50 and 56% were females [This study is not without limitations. First, we accrued participants by appealing to volunteers in an online research registry with access to email who were redirected to an online survey. Therefore, it is unclear what types of selection bias may apply to our cohort. However, this methodology likely led to our sample being more representative of the general United States pain population, compared to participants had they been accrued from the clinics of the sort of tertiary care centers where psychometric research is often conducted. Additionally, due to the randomized design of our study, any bias from the accrual method would be balanced between the two groups answering the questionnaire based on differing anchoring text. A second limitation to our study is that participants were randomized to separate surveys with one of the two anchor texts (between-subject randomization) rather than to the order of which survey with the anchor text they would first complete followed by the survey with the second anchor text (within-subject randomization). This would have doubled the number of surveys available for analysis and responses to both questionnaires would have been correlated, allowing us to test for minor differences in responses to the individual questions. However, this would have been at the cost of potential contamination (responses to the second survey being influenced by what subjects saw in the first survey). Another limitation of our study is that it is possible that, had we used another measure of creativity, our hypothesis that there would be differences in the relationship between anchor text and pain level based on self-perceived creativity may have been supported. Among our cohort, we found that 75% of participants considered themselves as being a creative person and nearly half of participants agreed that they were engaged in creative work on a regular basis. However, both of these estimates are high, suggesting that our measures of creativity were not particularly discriminatory. Nonetheless, rejection of the null (which we were unable to do in this study), would only further support the use of the “extremely severe pain” anchor text. Lastly, participants in our study were only reading and completing the questionnaire in English. While we would not anticipate issues around translations of the anchors in different languages, as with the BPI and other pain NRS being validated in various languages, this could be an area for further research. We also recommend additional studies examining a wider variety of anchor texts which may include cognitive interviewing as areas of future study.Our study is a rare example of comparative psychometric research. Normally, psychometric research is done on an individual instrument, with intra-item correlations, and correlations between scores and other patients’ aspects, calculated for a single instrument to determine whether it is psychometrically valid. Seldom do researchers compare the wording used in similar PRO instruments to determine which is better. In our current study, both approaches to pain assessment would be described as “valid” separately, but we found that the one with the anchoring text “extremely severe pain” has better properties than the other with the anchoring text “pain as bad as you can imagine.” This finding is only possible based on the randomized design. It is of note that studies comparing slight variations in language for scales need large samples. For instance, if the correlation between scale A and a variable is 0.45 but 0.3 for scale B, then a sample size of about 1,000 patients is needed for 80% power. Therefore, such studies have only recently been made feasible due the availability of electronic PROs and internet panels.