Objectives: The assessment of pain-related disability in pediatric chronic pain patients plays an important role in research on the effectiveness of pain treatment. The present study aimed to compare the 2 available measures of pain-related disability in the German language, the Functional Disability Inventory (FDI) and Pediatric Pain Disability Index (PPDI), in terms of psychometric properties and convergent validity. In addition, associations between FDI/PPDI scores and sex, age, and pain locations were investigated.
Materials and methods: Data of N=250 pediatric pain patients (Mage=14.4, SD=1.8) were collected at the patients' initial presentation to a specialized pediatric pain center.
Results: The results revealed similarly sound psychometric properties in terms of model fit, item difficulties, corrected item-total correlations, and missing values for both measures. However, item difficulties for the FDI were rather low. Both measures displayed good convergent validity in terms of associations with pain intensity, pain-related school absence, and emotional functioning (anxiety, depression). In both measures, girls had significantly higher scores than boys. No associations were found between the FDI/PPDI total scores and age or pain location.
Discussion: In conclusion, both measures are equally suited to assess pain-related disability in adolescents with chronic pain. The FDI should be used with caution in epidemiological studies due to the risk of floor effects. Further research is needed with regard to the relationship between pain-related disability and sex.