Purpose
The King-Devick (K-D) test is a rapid number naming test that has been studied extensively as a marker of neurological disease and concussion. Potentially confounding variables have not been studied in a large sample. The purpose of this study was to determine important confounding variables that are associated with K-D test performance.
Methods
In this cross-sectional, multi-center study, subjects ≥15yrs old with binocular near visual acuity < 20/30 completed two trials of the K-D test protocol. Exclusion criteria included concussion within 3-months, post-concussion syndrome, dyslexia or neuro-degenerative disorders. History of concussion, amblyopia, strabismus as well as demographic variables of education, race/ethnicity, gender and age were assessed by subject interview. Multiple linear regression analysis was performed. Independent variables were modeled as categorical (age (< or > 40 years), race/ethnicity, gender, education, concussion, amblyopia, strabismus) and continuous (age in years greater than 40 years) terms.
Results
Subjects (n=691, age 39.8±17.7 years) were enrolled across 5 sites. The average best K-D time was 41.2±8.2s. Table 1 shows the results of multiple regression analysis. The final multiple regression model included age beyond 40 years, education, black race and Hispanic race. With other variables held constant, the K-D test time worsened by 0.27s for each year in age above 40, improved by 1.94s for each category of higher education level achieved, worsened by 3.67s for black race and improved by 2.38s for Hispanic ethnicity. Gender, White race, Asian race, amblyopia, strabismus, or history of concussion was not associated with K-D test performance.
Conclusions
Age greater than 40 years, education, black race and Hispanic ethnicity were significantly associated with K-D test performance. Knowledge of these confounding variables is important for applications of K-D test in neurologically diseased populations and its development as a clinical measurement tool.