"Research in 1969 by J. J. Leeming showed countries driving on the left have a lower collision rate than countries driving on the right, although he acknowledged that the sample of left-hand rule countries he had to work with was small, and he was very careful not to claim that his results proved that the differences were due to the rule of the road. It has been suggested this is partly because humans are more commonly right-eye dominant than left-eye dominant. In left-hand traffic, the predominantly better-performing right eye is used to monitor oncoming traffic and the driver's wing mirror. In right-hand traffic, oncoming traffic and the driver's wing mirror are handled by the predominantly weaker left eye. In addition, it has been argued that left-sided driving is safer for elderly people given the likelihood of their having visual attention deficits on the left side and the need at intersections to watch out for vehicles approaching on the nearside lane. Furthermore, in an RHD car with manual transmission, the driver has the right hand, which for most people is dominant, on the steering wheel at all times and uses the left hand to change gears and operate most other controls."