In Wareland last year, 16 percent of licensed drivers under 21 and 11 percent of drivers ages 21-24 were in serious accidents. By contrast, only 3 percent of licensed drivers 65 and older were involved in serious accidents. These figures clearly show that the greater experience and developed habits of caution possessed by drivers in the 65-and-older group make them far safer behind the wheel than younger drivers are.

Which of the following is an assumption on which the argument depends?