It was brought to our attention that evaluation of the upper cutpoint of the clock drawing systems should have been based on detecting safe driving as the outcome of interest, whereas evaluation of the lower cutpoint should have been based on detecting unsafe driving as the outcome of interest. The current ROC curve listed in Table 2 is for evaluating “safe driving” as an outcome, and not “unsafe driving” as currently listed in the title. Please make this correction to the title of Table 2. Incidentally, the ROC curve for evaluating “unsafe driving” as the outcome of interest can be found by reversing the sensitivity and specificity columns of Table 2, so not both ROC curves need to be included in the paper.
Subsequently, the text in the last paragraph of the Results section on page four should read as follows:
“… .rating of road-test performance. Furthermore, although the upper cut score was highly specific in detecting safe driving, reliably classifying safe drivers 93% of the time (13/14 drivers who scored >6 passed the road test; positive predictive value = 0.93, negative predictive value = 0.43), the use of a lower cut score was insensitive in detecting unsafe driving, only classifying unsafe drivers accurately 53% of the time (8/15 drivers who scored <3 failed the road test; positive predictive value 0.53, negative predictive value 0.63).”
Please note these edits do not change the conclusions of the paper.