I am confused about how to calculate these 2 parameters, for example if we have 100 new cases, total population 1000. Some books say incidence should be number of the new cases divided by the number of the total population AT RISK. It means 100/ 1000-100 which 100/900 because they consider only 900 are at risk as the 100 new cases already have the disease. Other books just divide 100 by 1000. In first aid they put that comment about incidence only (When calculating incidence, don't forget that people currently with the disease, or those previously positive for it, are not considered at risk).
So which method should we use for the exam and does it apply for incidence and not for prevalence ?
So which method should we use for the exam and does it apply for incidence and not for prevalence ?