Reliability of novice and experienced physiotherapists using the normalized navicular height truncated and the foot posture index-6 for classifying static foot posture in adults

[Purpose] To investigate the reliability of novice and experienced physiotherapists using the normalized navicular height truncated and the foot posture index-6 for classifying foot posture in healthy adults. [Participants and Methods] Thirty asymptomatic adults participated in this study. After brief training, inter-rater reliability was performed by an expert and inexperienced rater (the novice physiotherapist). On the same day, both raters independently performed the normalized navicular height truncated and the foot posture index-6. For intra-rater reliability, the inexperienced rater repeated data collection on the 8th day after the first assessment. Intraclass correlation coefficients (ICCs) and Cohen’s Weighted Kappa (K(w)) were used for continuous and categorical data, respectively. [Results] The normalized navicular height truncated and the Rasch-converted foot posture index-6 scores demonstrated an excellent inter- and intra-rater reliability (ICCs=0.98–0.99). For classifying foot posture, the normalized navicular height truncated and the total foot posture index-6 scores represented more than 90% inter- and intra-rater agreement with K(w) values ranging from 0.92–0.94, while each item of foot posture index-6 demonstrated inter- and intra-rater agreement ranging from substantial to almost perfect (K(w)=0.71–0.94). [Conclusion] The normalized navicular height truncated and the foot posture index-6 are simple and reliable methods that can be used by the inexperienced rater.