Let us consider two kinds of population. At first let’s say, a population has around a thousand members. Let 400 of these people have a particular disease but around 100 of them died from the same disease and same time frame. Therefore, here the mortality rate is 100/ 1000 or 10% mortality rate. The other rate will be 100/400 or 25% case Fatality Rate. Let us consider the second population to be 1000 as well. Let 40 people suffer from a disease and 20 die from the same. Hence, the mortality rate will be 20/1000 or 2% and the fatality rate will be 20/40 or 50%. Hence the severity is greater in the second case. While death incidence is higher in the first population.