Functional Symmetry Observation Scale, Version 2: Reliability, Construct Validity, and Potential for Clinical Use

Abstract

Purpose: To examine the intrarater and interrater reliability and construct validity of the Functional Symmetry Observation Scale, Version 2 (FSOS-V2) in infants with congenital muscular torticollis (CMT). Methods: The FSOS-V2 is a video-based measure of postural and movement symmetry in infants with CMT. Four examiners scored 50 participants’ videos twice. Scores obtained by the same rater and across 4 raters were compared to examine intrarater and interrater reliability, respectively. Participants’ habitual head deviation from midline in supine photographs was measured using a protractor. Relationship between the head tilt angles and FSOS-V2 scores was examined to assess construct validity. Results: Fifty infants with CMT, age range 1 to 16 months, participated. Results indicated moderate to good intrarater and poor to moderate interrater reliability. The FSOS-V2 construct validity was supported. Conclusion: The FSOS-V2 can be used by the same therapist repeatedly to make clinical decisions. Further research will strengthen its psychometric properties.