PREPRINT: Assessing chronic pain processes longitudinally: Part 2 - Psychometric evaluation of the German “Assessing Chronic Pain Processes” (ProCEss) item set

Background. Ecological Momentary Assessment (EMA) is gaining relevance in contemporaneous pain research. However, EMA questionnaires are rarely psychometrically evaluated, potentially compromising data quality. This study aimed to develop and evaluate a German item set assessing psychological chronic pain processes for use in EMA, focusing on variability and reliability. Methods. First, the item set was piloted with three people suffering from chronic pain to gather feedback on participant burden and the usability of the data. Second, an evaluation was conducted with a sample of n = 68 individuals with lived experience of chronic pain who completed an EMA protocol with six assessments per day over twelve days (4,236 datapoints). Third, revised parts of the item set were preliminarily evaluated in n = 10 people suffering from chronic pain over a 21-day EMA period with six assessments per day (1,253 datapoints). Variability was examined primarily using within-person standard deviations and response distributions. Reliability was assessed according to current recommendations for single-item measures (test-retest reliability), two-item scales (Spearman-Brown coefficient), and multi-item scales (McDonald’s Omega).Results. Most items and process scales met the predefined criteria for variability and reliability. However, variance was largely attributable to between-person differences. Four out of thirteen scales demonstrated insufficient reliability.Conclusions. This study presents the first psychometrically evaluated German EMA item set capturing a broad range of clinically relevant pain processes. While the findings are promising, further refinement of several scales and additional psychometric evaluation are warranted.