its really Simple bro...
basically they study on 100 vehicles of each company for # of probz.
the # you see after each company is actually # of probz ,
so lexus being most reliable and in 100 lexus reported probz were 136 and for 100 Rovers 438 probz reported.
it was conducted for all cars of that company for the year of 2006.
hopes it is clear now.