The effects of multiple medical conditions on the risk of Quebec drivers being involved in a motor vehicle crash

Three major studies have examined the influence of medical conditions upon crash risk. (Monash report, Charlton et al (2010); Vaa (2003); Vernon et al (2002)). These large studies reveal that some medical conditions are associated with higher risk of an adverse driving event, crashes and infractions, than others. A previous paper of the authors on crash risk for Quebec drivers with a medical condition demonstrated that there are increases to crash risk according to the number of medical conditions that are present (see also 01528271). In this paper, this phenomenon is investigated in more detail: The objective of this phase of the Quebec study is to examine the effects of multiple medical conditions on the risk of drivers having a crash involving injury or death. The results revealed that female drivers with multiple medical conditions have crash risks that are consistently higher than their male counterparts. For female drivers the incremental increase in crash risk for each additional medical condition is double that for males with the same number of medical conditions. However, when comparing males to females it should be borne in mind that the crash risk for a male with no medical conditions is 1.60 times greater than his female equivalent. Thus, although the female drivers may have higher odds ratios, the number of crashes in which they are involved may be fewer than those of their male counterparts. Contrary to the other age groups, the crash risk does not increase for the over-65 age-group with more than 3 conditions. These results underline the importance for licensing agencies of identifying younger drivers with multiple medical conditions.