I am talking about computer science. Recently I did survey on my own i mean informally. I find out that there are some researchers who were able to do PhD in same area in 4 year as compare to other researcher who did their PhD in 6 or 6.5 year's in the same research area. Is it depends upon the duration of the PhD of supervisor or it depends upon the country etc.
Question : Why does a PhD take a longer time in some countries? What factors affect this? Does it affect the research quality? I mean if I am taking more time I should have more quality research.