Duration of residency is specialty dependent and varies by the scope of the competencies expected from the specialist after the training. I think the shortest residency duration may be 4 years.
I am not aware of any study that had tested the effect of duration of training on the quality of the trainee; such study promises to be very revealing, if well designed.
The duration of residency training in Nigeria is speciality dependent ranging from 4 to 6 years. The duration in each specialty is carefully chosen putting into consideration the scope of that specialty to cover. Skill acquisition especially in surgical related specialties is very important. A surgical resident needs to acquire surgical skills and proficiency is duration and no of cases done or assisted dependant.
As to whether the current duration is short or long? IN MY opinion I think the current duration is optimal evidence to support my opinion is with the fact that our products are not doing badly within and outside the country after training in Nigeria. Some excel outside the country when exposed to better enabling environment. I have not come across clear published evidence on the duration of residency however, we have witnessed that those that overstay in residency turn out to be better skillfuly because of prolonged exposure to skill acquisition and training compared to their colleagues that pass their exams at once.