The Functional Disability Inventory (FDI) is a well-established and commonly used measure of physical functioning and disability in youth with chronic pain. Further validation of the measure has been called for, in particular, examination of the clinical utility and factor structure of the measure. To address this need, we utilized a large multicenter dataset of pediatric patients with chronic pain who had completed the FDI and other measures assessing pain and emotional functioning. Clinical reference points to allow for interpretation of raw scores were developed to enhance clinical utility of the measure and exploratory factor analysis was performed to examine its factor structure. Participants included 1300 youth ages 8 to 18 years (M=14.2 years; 76% female) with chronic pain. Examination of the distribution of FDI scores and validation with measures of depressive symptoms and pain intensity yielded three distinct categories of disability: No/Minimal Disability, Moderate Disability and Severe Disability. Factor analysis of FDI scores revealed a two-factor solution representing vigorous Physical Activities and non-physically strenuous Daily Activities. The three-level classification system and factor structure were further explored via comparison across the four most commonly encountered pain conditions in clinical settings (head, back, abdominal and widespread pain). Our findings provide important new information regarding the clinical utility and validity of the FDI. This will greatly enhance the interpretability of scores for research and clinical use in a wide range of pediatric pain conditions. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Conflict of InterestThe authors have no financial or other relationship that might lead to a conflict of interest. NIH Public Access Author ManuscriptPain. Author manuscript; available in PMC 2012 July 1. In particular these findings will facilitate use of the FDI as an outcome measure in future clinical trials.Assessment of pain-related disability is an essential component in the evaluation and treatment of pediatric patients with chronic pain. The Functional Disability Inventory (FDI) [40] is one of the most widely used measures of functional impairment among children and adolescents with chronic pain, and its initial psychometric properties have been well established [3,26]. The FDI is a brief 15-item instrument originally developed to assess disability in children and adolescents with chronic abdominal pain [41,3]. Subsequently it has been used with a variety of pediatric chronic pain conditions such as fibromyalgi...

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The current study aimed to validate the child and parent pain catastrophizing scale in a large chronic pain sample and to identify child pain catastrophizing clinical reference points. Patients and parents (n= 697) evaluated at a pediatric pain program completed the Pain Catastrophizing Scale, child (PCS-C) and parent (PCS-P) report, along with additional measures of psychological functioning. The measure’s psychometric properties were examined, as well as relations across demographic, pain, and psychological characteristics and pain catastrophizing. Clinical reference points were identified for the PCS-C from differences in pain catastrophizing across levels of disability, depressive symptoms, and anxiety. Overall, we did not find support for the hypothesized three-dimension structure and recommend potentially removing items 7 and 8 for both the PCS-P and PCS-C due to floor/ceiling effects. The 11-item PCS-C is most parsimonious as a unitary construct, while the 11 item PCS-P is comprised of two factors. Although parent catastrophizing was significantly associated with child outcomes after controlling for pain level, it was no longer significant when accounting for child catastrophizing. When comparing PCS-C scores based on child outcomes, significant differences emerged for low, moderate, and high catastrophizing levels. It appears that the influence of parent catastrophizing on outcomes can be explained through its impact on child catastrophizing levels. Lastly, PCS-C reference points derived from this large sample can aid clinicians in assessment and treatment planning, in turn increasing the utility of the PCS-C for both clinical and research purposes.