Reliability and validity of the foot and ankle outcome score: a validation study from Iran

The aims of this study were to culturally adapt and validate the Persian version of Foot and Ankle Outcome Score (FAOS) and present data on its psychometric properties for patients with different foot and ankle problems. The Persian version of FAOS was developed after a standard forward-backward translation and cultural adaptation process. The sample included 93 patients with foot and ankle disorders who were asked to complete two questionnaires: FAOS and Short-Form 36 Health Survey (SF-36). To determine test-retest reliability, 60 randomly chosen patients completed the FAOS again 2 to 6 days after the first administration. Test-retest reliability and internal consistency were assessed using intraclass correlation coefficient (ICC) and Cronbach's alpha, respectively. To evaluate convergent and divergent validity of FAOS compared to similar and dissimilar concepts of SF-36, the Spearman's rank correlation was used. Dimensionality was determined by assessing item-subscale correlation corrected for overlap. The results of test-retest reliability show that all the FAOS subscales have a very high ICC, ranging from 0.92 to 0.96. The minimum Cronbach's alpha level of 0.70 was exceeded by most subscales. The Spearman's correlation coefficient for convergent construct validity fell within 0.32 to 0.58 for the main hypotheses presented a priori between FAOS and SF-36 subscales. For dimensionality, the minimum Spearman's correlation coefficient of 0.40 was exceeded by most items. In conclusion, the results of our study show that the Persian version of FAOS seems to be suitable for Iranian patients with various foot and ankle problems especially lateral ankle sprain. Future studies are needed to establish stronger psychometric properties for patients with different foot and ankle problems.