Objectives: In the postoperative setting, functional interference of pain is an important outcome parameter. It can be measured by numerical rating scales (NRS) and by binary items (yes/no). For implementation, dissemination, and practicability in clinical routine, not only psychometric characteristics but also patients' acceptance of assessment methods is important but has not been studied so far. To compare these 2 answer formats, the pain interference questions of the German initiative Quality Improvement in Postoperative Pain Management, a multicentric pain registry project, were used.
Methods: Psychometric quality, clinical significance, and patients' preferences were analyzed in NRS and binary formats of pain interference assessments. Responses from 430 patients in 3 surgical disciplines (abdominal, orthopedic/trauma, and oromaxillofacial surgery) were examined.
Results: The results indicate a satisfactory reliability and validity of both answer formats. They achieve equal test-retest reliability (0.724 to 0.885) and construct validity (identifying significant differences between the 3 surgical disciplines). The binary "no interference" answer consistently corresponds to NRS values of 0 to 2. The means in 3 pain intensity measures differ significantly for the groups of patients with or without pain interference. Two third of the patients prefer to answer to binary items.
Discussion: Binary answer format was proven to be a practical alternative to the NRS format for a screening instrument. Comparison of binary answers with NRS answers can improve our understanding of the clinical relevance of patients' statements. Most patients prefer the use of the binary answer format.