a Demonstration of how the non-linear regression model works to find the inflection/change points. b, c Plots of correlation in the scores between two trials (in the same test sitting) as the testing time progresses for HV (n = 22) and MS (n = 119). Orange lines represent the underlying non-linear regression models fitted to the data. Dotted lines indicate the minimum time needed for reliable performance based on the non-linear regression algorithm. Dashed lines point to the correlation coefficients at 75 s, or the time constraint that was eventually implemented. Blue lines indicate that after 75 s, the correlation continues to slightly improve. d Comparison of testing speed, in points per seconds, within the same trial at 75 and 90 s. Individuals show strong evidence of increasing their speed towards the end of the test (p < 0.001) but the change of 0.003 points/s is clinically insignificant.