What factors influence ratings of Global Perceived Effect by individuals with low back pain and physiotherapists?

The Global Perceived Effect (GPE) scale is widely used to evaluate perceived improvement in individuals with low back pain (LBP). However, factors that influence GPE ratings by patients and physiotherapists remain unclear, particularly whether ratings reflect changes in pain, or psychosocial factors, or are more influenced by current health status. Thus, the objective of this study was to (1) examine the association and agreement between patient- and physiotherapist-rated GPE scores, (2) examine relationship between changes in clinical and psychosocial factors and GPE ratings, and (3) determine whether post-treatment scores or change scores better predict GPE ratings. This study was a secondary analysis of WELBack data, including 425 individuals with chronic non-specific LBP who received motor control or graded activity exercise. Outcomes were collected at baseline and 2-months post-intervention. GPE was rated by patients and physiotherapists. Correlation, Bland-Altman and kappa analyses were used to assess agreement. In regression models, dependent variables were patients' and physiotherapists' GPE ratings, and independent variables included pain, disability, function, quality-of-life, and psychosocial factors. Moderate agreement (ρ=0.6, κ=0.37) was found between patient's and physiotherapist's GPE scores. For patients, the most explanatory model (pseudo-R²=0.3) included pain, disability, function, and psychosocial factors. The physiotherapist model (pseudo-R²=0.1) included pain, disability, function, and quality-of-life. Both models fit better with post-intervention than change scores. In conclusion, patients' improvements were associated with changes in psychosocial factors additional to pain, disability and function, whereas physiotherapists place less emphasis on this domain. Post-intervention scores related more strongly to GPE, suggesting current status determines perceived recovery more than recalled change.