All data were analyzed according to the intention-to-treat principle. Differences in the primary outcome were analyzed with the use of an unadjusted chi-square test. Results are presented as absolute and relative risks and 95% confidence intervals. Kaplan–Meier curves for estimated survival were compared with the use of a log-rank test. A Cox proportional-hazards regression model was used to evaluate the influence of potential confounding factors on the outcome (factors were selected if the P value in the univariate analysis was <0.20).

The method described above is the most common and simplest way to measure one's vertical jump, but other more scientifically accurate methods have been devised. A pressure pad can be used to measure the time it takes for an athlete to complete a jump, and then using a kinematics equation (h = g Ă— t2/8),[4] the computer can calculate his or her vertical jump based on the time in the air.