Are not all dyslexics created equal?
These results suggest that treatment strategies for dyslexics may need to be modified to take into account their specific subtype.
The overlap may not be of concern if the result is significant or if the subgroup is<10% of the whole population, but if the overlap is greater than 10% it should not be ignored. The easiest way of allowing for overlap is to use a correction factor, calculated from the amount of overlap, to adjust analyses that ignore overlap.