32 Chapter 2 video cameras (JVC Everio GZ-HM300, JVC, Yokohama, Japan) capturing video at 30 fps and set up at a distance of 3 meters from the front and from the left side. The process was repeated until the participant had completed all four exercises and recordings were successfully collected. Subsequently, two physical therapists were asked to view the video recordings and rate the quality of performance of the exercises by the participants. The physical therapists both had 10 or more years of experience treating patients with LBP, but they worked in different settings. The first physical therapist worked in a healthcare center, and the second physical therapist worked in a primary care physical therapy practice. After one week, the first physical therapist repeated the process to complete data collection. Data analysis A priori, a sample size of 50 participants for both the validity and the reliability testing was used in accordance with the recommendations made for a good rating by the COSMIN initiative (27). All analyses were performed using IBM SPSS Statistics for Windows, Version 23.0 (Armonk, NY: IBM Corp). All data were anonymized before analysis. Personal and demographic characteristics Descriptive statistics were applied to describe the samples for the validity and reliability studies. For continuous data, means and standard deviations were calculated. For categorical data, percentages were calculated instead. Validity Validity was assessed using Spearman’s rho for the correlations, as all comparator data were collected using ordinal scales. As no gold standard exists for the measurement of adherence to HBE recommendations, it was decided a priori that at least three of the four predetermined hypotheses would need to be accepted to confirm the validity of the EXAS. Reliability Intrarater and interrater reliability were assessed using Cohen’s kappa with quadratic weights (28). Additionally, the 95% confidence interval was calculated. Results were interpreted using the guidelines proposed by Cicchetti and Sparrow (1981) (29). These guidelines state that kappa scores: below 0.40 are poor; between 0.40 and 0.59 are fair; between 0.60 and 0.74 are good; and between 0.75 and 1.00 are excellent.
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