Journal of Pediatric Psychology Advance Access published January 6, 2016

Journal of Pediatric Psychology, 2016, 1–20 doi: 10.1093/jpepsy/jsv161 Systematic Review

Systematic Review: Issues in Measuring Clinically Meaningful Change in Self-Reported Chronic Pediatric Pain Intensity John V. Lavigne,1,2,3 PHD, ABPP Department of Child and Adolescent Psychiatry, Ann & Robert H. Lurie Children’s Hospital of Chicago, 2Feinberg School of Medicine, Northwestern University, and 3Mary Ann and J. Milburn Smith Child Health Research Program, Children’s Hospital of Chicago Research Center All correspondence concerning this article should be addressed to John V. Lavigne, PHD, Ann & Robert H. Lurie Children’s Hospital of Chicago, 225 East Chicago Avenue, Chicago, IL 60611, USA. E-mail: [email protected] Received July 25, 2015; revisions received November 28, 2015; accepted December 1, 2015

Abstract Objective This report examined limitations in our ability to assess clinically significant change (CSC) in randomized controlled trials of treatments of self-reported pediatric chronic pain intensity. Methods The following were reviewed: (a) approaches to assessing CSC; (b) approaches to assessing CSC used in psychological treatment studies of self-reported pediatric chronic pain intensity included in a recent systematic review; (c) the role of test–retest reliability in distribution-based CSC measures; (d) the test–retest reliability of recommended chronic pain measures. Results and Conclusions Existing studies do not assess whether a CSC occurred or use procedures that did not account for measurement error and true score fluctuations unrelated to treatment, possibly resulting in overestimating CSCs. Distribution-based approaches to assessing CSCs that address these problems require knowing test–retest reliability of the chronic pain measure at appropriate intervals. Available information raises concern about our ability to estimate CSC reliably. Recommendations are made for future research.

Key words: clinical significance; chronic and recurrent pain; pain.

Pain is a complex phenomenon with distinct domains that include pain intensity, physical functioning, symptoms, and emotional functioning, among others (McGrath et al., 2008; Norman, Sloan, & Wyrwich, 2003; Palermo, 2009). Clinical trials of the treatment of chronic pediatric pain rely on selfreports of pain as a key outcome measure. Few areas of medicine rely as heavily on self-report for clinical diagnosis (Miro, 2009), and self-reported chronic pain intensity remains the single most common measure of intervention response in pediatric pain studies (Palermo, 2009; von Baeyer, 2009). Singleitem self-report measures of chronic pediatric pain intensity are commonly used (Stinson, Kavanaugh, Yamada, Gill, & Stevens, 2006), and are

recommended for use in measuring that construct (McGrath et al., 2008). While psychologists have long been using selfreports to assessing change in patient’s affect and behavior, in some areas of medicine, the emphasis on measuring treatment response using Patient Reported Outcomes (PROs) when biomarkers are not available has increased. This is true for measuring outcomes for all pediatric chronic illnesses, for example, quality of life (Bevans, Riley, Moon, & Forest, 2010), and certainly includes the measurement of pain in response to treatment (Food and Drug Administration, 2012). Accordingly, there has been increased interest in ways of assessing change in randomized controlled trials (RCTs) in which PROs are used.

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Approaches to Measuring CSC While estimating the statistical significance and ES of an intervention occurs at the group level (treatment vs.

comparison group), determining whether a CSC has occurred involves patient-level analysis, that is, determining whether each study participant has achieved a CSC. Approaches to assessing CSC include anchorbased and distribution-based (Cella, Eton, Lai, Peterman, & Merkel, 2002; Copay, Subach, Glassman, Polly, & Schuler, 2007), percent-change (Dworkin et al., 2008), statistical (Jacobson & Truax, 1991), and combined approaches (Crosby, Kolotkin, & Williams, 2003). See Table I for a summary of these approaches.

Anchor-Based Approaches Anchor-based methods map a difference score on a continuous measure to a patient’s verbal “anchor” of “improved,” “better,” etc. (Cella et al., 2002). That difference score becomes the minimum clinically important difference (MCID), that is, the smallest change important to the patients (Copay et al., 2007). For example, if the mean score for pre- to posttreatment change on a visual analogue scale (VAS) associated with children’s ratings of “better” is 23.00 mm, that value is the MCID, and scores 23.00 mm are considered clinically significant. Presumably, that MCID value can then be used in similar situations to determine who has achieved a clinically meaningful change, but searching for a single, generalizable number may be unrealistic (Cella et al., 2002), especially when developmental factors, demographic differences, pain conditions, level of pain severity, etc. could influence the MCID. Pediatric studies of anchor-based MCIDs have been conducted (Bulloch & Tenenbein, 2002; Myrvik et al., 2013; Tsze et al., 2015). The anchor-based approach, relying on a global improvement scale (GIS) such as a self-report of better, appears face valid and is easy to interpret, but has considerable limitations. Norman, Stratford, and Regehr (1997) note that judging improvement requires that the individuals be able to quantify both their initial and present state, but adults have difficulty recalling their initial pain state. Similarly, children’s recollections of prior pain levels have been found to be poor (Chogle et al., 2012; van den Brink, BandellHoekstra, & Abu-Saad, 2001), raising questions about the child’s ability to accurately use such a GIS as a “better” rating. In addition, the reliability of rating “better” or “improved” is unknown and, in general, there is little evidence supporting strong test– retest reliability of global scales to measure change (Norman et al., 1997). If the anchor used to quantify the MCID may not be reliable, the MCID value for the continuous measure may not be reliable. Furthermore, if the GIS itself were reliable, quantifying the MCID would be unnecessary (McCarthy,

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In addition, while statistical significance was once the only criteria applied to determining whether research findings were meaningful, more emphasis is now being placed on the importance of assessing the magnitude of the observed effect (American Psychological Association, 2010). This can take the form of reporting an effect size (ES), but could also take the form of reporting a measure of clinical significance. Different approaches have been taken to assessing the clinical significance of treatment, and the psychometric properties of the measures used in assessing change can influence how clinically significant treatment appears to be. Along with the potential clinical implications, there are also policy implications associated with assessing clinically significant change (CSC). For clinical trials of treatment for the functional disorder of irritable bowel syndrome (IBS), for example, the FDA (Food and Drug Administration, 2012) has recommended using a measure of self-reported clinical significance based on the percent change in pain reported by the individual. RCTs of medications to treat this condition are expected to use a standard of 30% in pain symptoms as one outcome criteria for success; as we shall see, the reliability of findings based on that approach to measuring symptom change may be less reliable than alternatives. Presently, it is important to assess what we know about different approaches to assessing clinically meaningful treatment outcomes, how psychometric properties of chronic pain intensity measures influence the measurement of clinical significance, and which approaches are likely to lead to studies that identify reliable, clinically significant psychological and pharmacological approaches to treating pediatric pain. The purpose of this review is to examine whether existing measure of chronic pain intensity that have been recommended for use in systematic reviews (Cohen et al., 2008; Stinson et al., 2006) or by expert panels (McGrath et al., 2008), or used in RCTs of psychological treatments of chronic pain in children and adolescents (Fisher et al., 2014), are suitable for assessing CSC in future RCTs. This report will discuss the following in the given order: (a) the strengths and weaknesses of approaches to measuring CSC in RCTs in which chronic pediatric pain intensity is an outcome measure; (b) how CSC has been measured in RCTs of psychological interventions for chronic pediatric pain treatment; (c) based on a systematic review, what we know about the test–retest reliability of chronic pediatric pain intensity measures recommended for use in prior reports as well as those used in clinical trials; (d) future directions in measuring CSC in studies of pediatric pain.

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Table I. Characteristics of Approaches to Measuring Clinically Significant Change (CSC) Approach

Core element

Anchor based

Global rating of “better,” Appealing face validity; easy to “improved,” etc.; may include obtain; multiple approaches to quantification of rating on a calculating MCID value continuous scale to calculate the minimal clinically significant difference (MCID)

Percent change

Cutoff score to classify as improved versus not improved based on a percent change from individual’s baseline score

b. Standard error of mean (SEM) approach Statistical

Combined

Number needed to treat (NNT)

Unlikely to be a single anchor-based MCID across ages, disorders, etc.; poor retrospective recall of initial state raises concerns about meaningfulness of rating; reliability of global rating of “better,” etc. is not known Appealing face validity as a Magnitude of change varies to meet marker for a minimum change; cutoff based on initial pain level; Food and Drug Administration may identify some individuals as recommended for some condiimproved when there reports are tions; often used for some disornot reliable ders, allowing comparisons across studies

Uses Cohen’s ES to specify cutoff for improved

ES familiar to scientific community

CSC determined based on the SEM in the sample/population

Using 1.96 SEM, 95% confidence that rating of improved vs. not improved is reliable Cutoff score likely to be meaningful

Defines the CSC based on change to a target level of the normal population (e.g., 2 weeks. Thus, we know little about the test–retest reliability of the VAS for the intervals that are common for pre–post or pre-followup assessments in RCTs in studies of psychological interventions. Drug trials often cover the same intervals, so relevant information for use with such studies is also lacking. Although the focus of this report has been on the problems of ascertaining test–retest reliability estimates that can be used to examine CSC in treatment studies of chronic pediatric pain, the effects of our limited knowledge of test–retest reliability for pain intensity measures applies to other types of conditions and other types of PROs. For example, acute pain resulting from an injury or surgical procedure could last for days or weeks. Variability in patient-reported pain intensity could result from variability in the underlying latent “true” level of pain and not just measurement error. A study designed to determine whether, say, a psychological intervention reduced acute pain a week after a particular surgical procedure was conducted would need to know what the test–retest reliability for that condition was for the tested interval to determine in CSC resulted from treatment. It is less clear how problems with variability in latent “true” levels of pain might affect studies of treatments for procedural pain. The true level of pain associated with, say venipuncture, is likely to diminish over time, but the diminution in latent true pain intensity might be rapid enough that it adds little to variability above measurement error. As the studies in Table III indicate, we know no more about the test–retest reliability of these measures when they are used to assess acute or procedural pain that we do about chronic pain. How changes in latent true pain levels vary is, of course, a question that requires empirical verification. There is also an important pragmatic aspect to the use of test–retest reliabilities. Requiring that someone be considered a responder based on a combined statistically reliable change and CSC sets a high bar for deciding that a treatment is successful. Studies using that standard to determine treatment success may require larger sample sizes than studies assess whether treatment and control groups differ on a continuous measure in the manner typically used in RCTs. While such studies may be more difficult to conduct, their findings may be more meaningful and

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reliability can be used to establish the criterion for a reliable change with only a 5% chance that classification of responders is not statistically reliable. Methods combining the need to achieve a reliable change with a criterion for clinical significance (“better” using an anchor-based approach, a meaningful percent change criterion, or statistical criteria for clinical significance) provide the best way to ensure accurate classification as both reliable and clinically significant. The limitations of our understanding of the test– retest reliability of recommended measures of chronic pediatric pain intensity, however, make it difficult for researchers to assess reliable CSC in studies of pediatric pain intensity at this time. The limitations are both conceptual and empirical. Conceptually, it is known that the magnitude of test–retest reliability coefficients is reduced not only by measurement error but also by true score fluctuations that vary over time. It is clear from reports on the use of distribution-based measures of clinical significance that they were intended to be used with traits or symptoms showing such fluctuations in true scores, such as quality of life (Cella et al., 2002) and marital satisfaction (Jacobson & Truax, 1991). It is not uncommon for the magnitude of test–retest reliability coefficients to decline as the interval between measurement points increases. As a result, to estimate true score fluctuations, it seems appropriate that the test–retest reliability used to calculate a CSC should approximate the interval between test administrations in the RCT, that is, the interval between pre- and posttreatment assessments, and between pretreatment and follow-up. Using the reliability coefficient for a short interval will inflate the clinical significance of a treatment that takes 4–12 weeks to administer, while a coefficient from a longer time interval may lead to underestimating the intervention’s clinical significance. This issue has not been well-discussed and warrants further attention. Empirically, this review indicates that we lack sufficient information about the test–retest reliability of existing pediatric pain intensity measures to be able to calculate statistically reliable, clinically significant estimates of treatment effectiveness for psychological interventions for chronic pain as this time. In the studies reviewed by Fisher et al. (2014), the pre–post treatment interval varied widely, with most treatments occurring over 3–12 weeks, and the posttreatment to follow-up period from 3 to 12 months. Presently, we have no studies of the test–retest reliability that could be used in determining CSCs for any recommended measure of pediatric pain intensity for any intervals that are similar to those used in RCTs for psychological interventions for chronic pediatric pain. For the VAS, some data are available on short intervals that may be useful in studying pre- to posttreatment CSCs. Test–retest reliability for 1-week interval has been

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trial. Studies would be needed to determine whether test–retest reliabilities differ for treated versus untreated control groups. For disorders that occur with some regularity in the general population (e.g., abdominal pain, headache), estimates of test–retest reliability in general populations may be useful, but it is not known if they differ for a community, nonclinical sample from those with chronic conditions. There has been considerable interest in the use of electronic diaries for measure pain. Presently, attention has focused on the feasibility and acceptability of this technique (Palermo, Valenzuela, & Stork, 2004; Peters et al., 2000; Stinson, 2009), but attention to the reliability of such measures needs to be addressed, as well, if they are to play an important role in assessing reliable, clinically significant outcomes in future studies. Both paper and electronic diaries are often used for a week or so at each pretreatment, posttreatment, and follow-up assessment period in the course of the RCT. This may reduce the likelihood of recall error for that period compared with asking the child or adolescent what his or her usual or worst pain was during that interval. For the purpose of statistical analysis, those diaries are typically summarized into a single score for each assessment interval, and as the review shows, the reliability of those weekly summary scores over longer intervals is not established, and weekly fluctuations in the pain experience may be considerable. It is possible that the test–retest reliability coefficient for the control or comparison group in the RCT being conducted is appropriate for calculating the RCI to be used in calculating the CSC for that particular study. The interval between test administrations would be the same as that for the treatment group and would control for any effect of the repeated test administration. It would be of interest to examine how the test–retest reliability of the control/comparison group might differ from that for a group that only took the pre- and posttest in the manner of a wait-list control group. It is now well recognized that there are different domains to pain than just pain intensity, and changes in these other domains may be important to measure in studying treatment outcomes. Further review will be needed to determine whether adequate information is available on test–retest reliability to assess CSCs on measures in these other domains, and additional research on this psychometric property for measures in these other domains is likely to be needed. The absence of information about test–retest reliability has clinical and policy consequences. Based on the studies of psychological treatments of chronic pediatric pain included in the Fisher et al. (2014) systematic review, we have reason to believe that those

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more reliable. Presently, there is general concern over the difficulty in medicine and social science in the frequency with which study results cannot be replicated (Ioannidis, 2005, 2008), and the contributions of measurement error to this problem may be substantial (Ioannidis, 2008). Possibly, replication would be easier to achieve if outcome measures were more rigorous, with greater assurance that outcomes were reliable. This would occur using distribution or combined approaches compared with approaches not requiring reliable estimates of treatment response. Further research is needed to examine the test– retest reliability of measures of chronic pediatric pain intensity. At the practical level, more information about test–retest reliability of pain intensity is needed to be able to assess the clinical significance of treatments. It is important for future studies to assess the differences that occur in test–retest reliability at different time intervals for measures of pain intensity. Without a clearer understanding of the differences in that statistic that occur, there can be no empirical basis for deciding the magnitude of changes that occur and, say, whether an estimate of test–retest reliability for 8 weeks may be applicable to a treatment taking 10 weeks to complete. In addition, different approaches to self-reporting chronic pain intensity can be taken. At different intervals (e.g., pretreatment, posttreatment, follow-up), a study participant might be asked to report how intense her pain is now, what was the worst pain she experienced during a particular time interval, or what the usual pain level was for that time interval. Such ratings could be supplied for 1 day or 1 week, or daily for multiple days, with the average for that interval used as the measure of pain intensity. Given how few studies assessed test–retest reliability for chronic pain using the measures that were reviewed, the differences in test–retest reliability and their impact on assessing CSC could not be examined in this report. Nonetheless, the differences in these approaches to measuring pain intensity are potentially important, and attention to the effects of these different approaches on the test–retest reliability of chronic pain intensity reports need to be examined in future studies. Information about test–retest reliability of chronic pain intensity measures is also needed for different disorders and developmental levels. Given the paucity of information currently available, we do not know how different the test–retest reliabilities are for this difference disease  developmental level groups. If such information were available, researches would be able to draw on such information in estimating sample sizes for designing RCTs with clinical significance as an end point. Lacking such information, clinicians may need to gather test–retest data during the clinical

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Recommendations These observations recommendations:

lead

to

the

following

1. To increase the likelihood that calculating CSC will result in reliable and clinically meaningful results, combined approaches to calculating CSC are preferable, particularly those that combine a distribution-based and statistical approach. 2. A nomological network of reports of test–retest reliability across different test administration intervals and with different ages and painful conditions needs to be developed. It will also be important to examine differences as a function of variations in test forms (e.g., different end point descriptors). This information is needed so that researchers can plan sample sizes for RCTs. 3. Until that network is developed, the best estimates of test–retest reliability that can be used in a particular study to calculate the CSCs will need to be based on those obtained for that particular study, using the test– retest reliabilities between administrations for the untreated control group for the intervals included in the study between assessment periods.

It is important to keep in mind that the empirical basis of support for the use of psychological interventions to treatment pediatric chronic pain has grown and is likely to continue to grow. As the field moves forward in its study of such interventions, better estimates of the clinical significance of such treatments will be important for the clinician and the consumer to know. Finding that the clinical significance of such treatments is good will be encouraging and, if the results are less reassuring, they may stimulate increased research leading to better treatments.

Supplementary Data Supplementary data can be found at: http://www.jpepsy. oxfordjournals.org/. Conflicts of interest: None declared.

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