# Casualty Analysis of the Drivers in Traffic Accidents in Turkey: A CHAID Decision Tree Model
## 5 Discussion  
In this study, as a non-parametric tree-based model, CHAID was employed to model the casualty levels of the drivers in traffic accidents involving only automobiles. The outcomes of this research obtained from the CHAID-tree algorithm identify the fact that alcohol usage, driver's age, education level of the drivers, and wet/slippery road surface profoundly affect the resulted accident severity. The results of the study conducted by [PERSON] to obtain the casualty level of the accidents by logistics regression state that snowy road surfaces increase the accident severity of the drivers compared to other types of road surface. In other studies, it has been found that drivers' casualty levels get worse with a rise in alcohol usage [49; 50]. The outcomes of this study in this sense comply with the findings from the literature. When the entire tree is thoroughly examined, male drivers were found to become involved in more accidents than women drivers, as it is probably a natural result of the fact that they undertake more travel/km than women. On the other hand, 71% of women drivers injure themselves rather than the other people in the accidents they cause. It can also be seen from the tree developed that 65% of the female drivers who do not adapt the vehicle speed to the road and weather conditions injure themselves at the intersections with four arms and roundabouts. It should be kept in mind that the four-arm intersections and roundabouts were combined in the same class and were evaluated together in the study. When it is observed through every leaf-terminal node with gender, it can be seen that the mortality rates of men in their own groups are more than the mortality rates of women in theirs. The same issue of male drivers' likelihood of having a tendency to become involved in fatal or injury-involving accidents was also stated in [PERSON] research [50]. Drivers' ages have been observed to have an effect on the casualty level of the accidents occurring at four-arm intersections, including roundabouts, as a result of excessive speed and illegal turns. In this regard, the finding of this research does not comply with the outcome obtained in [PERSON]'s study, in which it was found that the driver's age had no effect on traffic violation and accident severity [51]. Similarly, [PERSON] et al. stated in their study that the driver's age did not affect the injury severity level with the explanation that older and more experienced drivers' relatively careful and slow driving characteristics might tolerate and compensate the younger drivers' mistakes [52]. The findings undoubtedly exhibit the fact that the young drivers, especially those in the early years of having a driving licence, must be monitored and controlled to overcome the violations of the rules causing severe accidents in Turkey. The findings of this research revealed the fact that a slippery or wet road surface is an important factor affecting the severity of the accidents, even in the case of four-wheeled vehicles. A similar outcome was also obtained by [PERSON] for two-wheeled vehicles [5]. Accident reports kept by the police in Turkey do not include information on years of driving experience. In order to deepen the analysis with regard to the effect of the level of experience of the drivers on the severity level, information regarding the years that drivers have held a driving licence is important and, hence, must be recorded in the police reports. Even this information may not be sufficient because the duration and frequency of driving after obtaining a driving license are the factors that will affect the experience. As it may not be possible to obtain this information accurately from the drivers, it is a challenging issue to develop an accurate conclusion to evaluate the effect of driver experience on casualty levels. Similarly, a more comprehensive analysis would have been possible if, for example, the classification of injury level had been provided.