Doing this by brand seems to skew the numbers towards brands with model lineups that attract certain types of buyers, and their inherent behaviors, rather than

Doing this by brand seems to skew the numbers towards brands with model lineups that attract certain types of buyers, and their inherent behaviors, rather than on the merits of the vehicle. For example, the bottom of the list is not filled with brands with a lot of safety features, it is filled with brands that predominantly don't (/didn't) target riskier groups of drivers. People who buy boring vehicles drive differently than people who buy powerful and exciting vehicles. There is self-selection at play here.