To the Editor.—

Motor vehicle crashes are the most common cause of death among youth populations in developed countries in the world. Among initiatives developed to reduce motor vehicle crash–related injuries, deaths, and traffic convictions among youth, graduated driver licensing (GDL) laws have demonstrated effectiveness. In particular, a recent retrospective study by Chen et al indicated that GDL program components leading to reduced motor vehicle crash fatalities were GDL programs that include age requirements and ≥3 months of waiting before the intermediate stage, nighttime driving restriction, and either ≥30 hours of supervised driving or passenger restriction.

Although Chen et al provided a valuable contribution to the evidence base, they seem to have overlooked important variables that could affect their outcome (motor vehicle crash fatality), including vehicle miles traveled, vehicle density (number of registered motor vehicles divided by length of roads), speed-limit regulations, alcohol-impaired–driving laws (zero tolerance...

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