Left-handed people are more likely to suffer from immune disorders, such as allergies, than right-handed people
But left-handed people tend to have an advantage over right-handed people in accomplishing tasks controlled by the right hemisphere of the brain, and most people's mathematical reasoning ability is strongly influenced by the right hemisphere of the brain
The proportion of left-handed people whose mathematical reasoning ability is better than average is higher than that of those whose mathematical reasoning ability is weaker than average