King-Devick Test Reliability in National Collegiate Athletic Association Athletes: A National Collegiate Athletic Association-Department of Defense Concussion Assessment, Research and Education Report

Context: The King-Devick (KD) test has received considerable attention in the literature as an emerging concussion assessment. However, important test psychometric properties remain to be addressed in large-scale independent studies. Objective: To assess (1) test-retest reliability between trials, (2) test-retest reliability between years 1 and 2, and (3) reliability of the 2 administration modes. Design: Cross-sectional study. Setting: Collegiate athletic training facilities. Patients or Other Participants: A total of 3248 intercollegiate student-athletes participated in year 1 (male = 55.3%, age = 20.2 +/- 2.3 years, height = 1.78 +/- 0.11 m, weight = 80.7 +/- 21.0 kg) and 833 participated in both years. Main Outcome Measure(s): Time, in seconds, to complete the KD error free. The KD test reliability was assessed between trials and between annual tests over 2 years and stratified by test modality (spiral-bound cards [n = 566] and tablet [n = 264]). Results: The KD test was reliable between trials (trial 1 = 43.2 +/- 8.3 seconds, trial 2 = 40.8 +/- 7.8 seconds; intraclass correlation coefficient [ICC] (2,1) = 0.888, P < .001), between years (year 1 = 40.8 +/- 7.4 seconds, year 2 = 38.7 +/- 7.7 seconds; ICC [2,1] = 0.827, P < .001), and for both spiral-bound cards (ICC [2,1]= 0.834, P < .001) and tablets (ICC [2,1]=0.827, P < .001). The mean change between trials for a single test was -2.4 +/- 3.8 seconds. Although most athletes improved from year 1 to year 2, 27.1% (226 of 883) of participants demonstrated worse (slower) KD times (3.2 +/- 3.9 seconds) in year 2. Conclusions: The KD test was reliable between trials and years and when stratified by modality. A small improvement of 2 seconds was identified with annual retesting, likely due to a practice effect; however, 27% of athletes displayed slowed performance from year 1 to year 2. These results suggest that the KD assessment was a reliable test with modest learning effects over time and that the assessment modality did not adversely affect baseline reliability.