The Impairment and Functioning Inventory Revised-English version: A validation study in individuals with disabilities and bothersome pain.

Background: Despite the relevance of daily function in individuals with chronic pain, few questionnaires have been designed to assess this domain in individuals with musculoskeletal pain. In addition, the Impairment and Functioning Inventory-Revised (IFI-R) is the only instrument that assesses perceived decreases in levels of daily activity after the onset of pain.
Objective: To evaluate the psychometric properties of the English version of the IFI-R.
Design: Cross-sectional study.
Setting: A database of individuals with medical conditions commonly associated with chronic pain maintained by the University of Washington.
Patients: A total of 470 individuals with chronic pain.
Methods: Factorial validity was analyzed by conducting a confirmatory factor analysis via structural equation modeling. Internal consistency was evaluated by calculating Cronbach's α coefficients. Convergent validity was assessed by calculating Pearson correlation coefficients between the two scales of the IFI-R and the Patient Reported Outcome Measurement Information System (PROMIS) Pain Interference Scale. Criterion validity was analyzed by regression analysis via structural equation modeling.
Main Outcome Measures: The English version of the IFI-R (IFI-R-EV) for individuals with chronic pain.
Results: The IFI-R-EV consists of 30 items with two related subscales: The Daily Function subscale (α = .86). and the Impairment subscale (α = .89). A significant correlation was found between these subscales and a measure of pain interference (r's = - .33, and .35 respectively; p's < .01). We also found statistically significant associations (p < .05) between daily function and depression (β = -.14) and pain intensity (β = -.13), between impairment and depression (β = .14) and pain intensity (β = .16), and between daily function and pain acceptance (β = .14).
Conclusions: The findings indicate that the IFI-R-EV provides valid and reliable measures of daily function and impairment in English-speaking individuals with a disability and chronic pain. These results are consistent with those obtained with the Spanish version.
(© 2021 The Authors. PM&R published by Wiley Periodicals LLC on behalf of American Academy of Physical Medicine and Rehabilitation.)