Rasch Analysis of Reliability and Validity of Scores From the Foot and Ankle Ability Measure (FAAM)

Abstract

Background: The purpose of this study was to determine the reliability and validity of scores from the Foot and Ankle Ability Measure (FAAM) Activities of Daily Living (ADL) and Sports scales in patients who have a variety of ankle injuries. Methods: All patients who underwent surgical treatment for an ankle injury and completed the FAAM ADL and Sport scales were included in this study ( n = 456; 192 females, 264 males). The average age was 47.6 years (range, 18-79 years). The average time to follow-up was 3.8 years (range, 2.0-7.7 years). All data were collected prospectively and reviewed retrospectively. A reliability and validity analysis, utilizing the Rasch measurement model, a special case of item response theory (IRT), was conducted. Results: Reliability was very good. For FAAM ADL, person reliability was 0.87 and item reliability was 0.99. For FAAM Sport, person reliability was 0.89 and item reliability was 1.0. Infit mean square (MNSQ) values, which assess internal scale validity, were examined. For FAAM ADL, items 11 (coming up on your toes) and 10 (squatting) were high (2.27 and 2.08, respectively). All other infit values were within the acceptable range of 0.5 to 1.7. For FAAM Sport, all infit values were within the acceptable range. Outfit MNSQ values, which assess the FAAM ADL and Sport rating scale function, were examined. Three items from FAAM ADL were beyond the acceptable range. Items 10 and 11 from FAAM ADL had high outfit MNSQ values (2.15 and 1.98, respectively). Item 19 (light to moderate work) item had a marginally low outfit MNSQ of 0.48. For FAAM Sport, all outfit values were within the acceptable range. Conclusion: There was very good evidence of the reliability and validity of FAAM ADL and FAAM Sport scores. Two FAAM ADL items may indicate the need for further scale development for use in a diverse surgical ankle population. Level of Evidence: Level III, comparative series.