Events and eligible license days for these comparison drivers were counted at each functional ability level status. Only crashes and citations that occurred during the period of time the driver was licensed were considered. Citation, crash and at fault crash rates per eligible licensed driving day were calculated separately for restricted and unrestricted drivers with medical conditions and their corresponding drivers for each functional ability category. These data were then used to estimate the relative risk for each medical condition category, allowing a comparison of the crash or citation risk of drivers licensed with medical conditions to similar drivers licensed without medical conditions from the general driving population. The relative risk approximates a Chi-Square distribution with one degree of freedom.
Relative risk describes the influence of a particular variable on the likelihood of an outcome.
The second part of the project was an analysis of drivers with more than one medical diagnosis or medical condition. These drivers were therefore put into more than one functional ability category, and were assigned a functional ability level for each. Only a minority of drivers was listed in more than one functional ability category, and only a few of the possible combinations of functional ability categories occurred often enough to allow for meaningful analysis. Also, the numbers of drivers with two medical conditions was too small to allow for analysis by individual functional ability level. Manual Check of SubsetDeath certificates contain a code for cause of death.