Using confirmatory factor analysis to evaluate construct validity of the Brief Pain Inventory (BPI)

Context: The Brief Pain Inventory (BPI) is a frequently used instrument designed to assess the patient-reported outcome of pain. The majority of factor analytic studies have found a two-factor (i.e., pain intensity and pain interference) structure for this instrument; however, because the BPI was developed with an a priori hypothesis of the relationship among its items, it follows that construct validity investigations should use confirmatory factor analysis (CFA).

Objectives: The purpose of this work was to establish the construct validity of the BPI using a CFA framework and demonstrate factorial invariance using a range of demographic variables.

Methods: A retrospective CFA was completed in a sample of individuals diagnosed with HIV/AIDS and cancer (n=364; 63% male; age 21-92 years, M=51.80). A baseline one-factor model was compared against two-factor and three-factor models (i.e., pain intensity, activity interference, and affective interference) that were developed based on the hypothetical design of the instrument.

Results: Fit indices for the three-factor model were statistically superior when compared with the one-factor model and marginally better when compared with the two-factor model. This three-factor structure was found to be invariant across disease, age, and ethnicity groups.

Conclusion: The results of this study provide evidence to support a three-factor representation of the BPI, and the originally hypothesized two-factor structure. Such findings will begin to provide clinical trialists, pharmaceutical sponsors, and regulators with confidence in the psychometric properties of this instrument when considering its inclusion in clinical research.