Conceptual overlap of psychological constructs in low back pain.

The biopsychosocial model is increasingly accepted in low back pain (LBP) research and clinical practice. In order to assess the role of psychological factors in the development and persistence of pain, a wide array of measures has been developed. Yet there is likely to be considerable conceptual overlap between such measures, and consequently, a lack of clarity about the importance of psychological factors. The aims of this study were to investigate the extent of any such overlap. An observational cohort study of 1591 LBP patients consulting in primary care completed data on a range of psychological instruments. Exploratory and confirmatory factor analyses (EFA and CFA, respectively) were carried out at the subscale level (n=20) to investigate factor structure. The influences of the derived factors on clinical outcomes (pain intensity and self-reported disability) were then tested using linear regression. EFA yielded 4 factors, termed "Pain-related distress," "Cognitive coping," "Causal beliefs," and "Perceptions of the future," which accounted for 65.5% of the variance. CFA confirmed the validity of these factors models. The pain-related distress factor was found to have the strongest association to LBP patients' outcomes, accounting for 34.6% of the variance in pain intensity, and 51.1% of the variance in disability. Results confirmed that considerable overlap exists in psychological measures commonly used in LBP research. Most measures tap into patients' emotional distress. These findings help us to understand how psychological constructs relate together; implications for future research and clinical practice are discussed.