Are within-person numerical rating scale (NRS) ratings of breathlessness “on average” valid in advanced disease for patients and for patients’ informal carers?

Introduction: The Numerical Rating Scale (NRS) is frequently used to assess patient reported breathlessness in both a research and clinical context. A subgroup report average breathlessness as worse than worst breathlessness in the last 24 hours. The Peak/End rule describes how the most extreme and current breathlessness influence reported average. This study seeks to highlight the existence of a subpopulation who give ‘paradoxical averages using the NRS, to characterise this group and to investigate the explanatory relevance of the ‘Peak/End’ rule. Methods: Data were collected within mixed method face-to-face interviews for three studies: the Living with Breathlessness Study and the two sub-protocols of the Breathlessness Intervention Service Phase III randomised controlled trial. Key variables from the three datasets were pooled (n=561) and cases where participants reported a paradoxical average (n=45) identified. These were compared to non-cases and interview transcripts interrogated. NRS rating of average breathlessness were assessed for fit to Peak/End rule. Results: Patients in the paradoxical average group had higher Chronic Respiratory Questionnaire physical domain scores on average p=0.042). Peak/End rule analysis showed high positive correlation (Spearman’s rho= 0.756, p<0.001). Conclusions: The NRS requires further standardisation with reporting of question order and construction of scale used to enable informed interpretation. The application of the Peak/End rule demonstrates fallibility of NRS-Average as a construct as it is affected by current breathlessness. Measurement of breathlessness is important for both clinical management and research, but standardisation and transparency is required for meaningful results.