<unk> is a measure of disease frequency that counts the occurrence of new cases of disease that develop in a candidate population over a specified time period. It can be generally referred to as the risk of developing a new case. Although sometimes loosely expressed simply as the number of new cases during a specified time period, it is better expressed as a proportion or rate in which the calculation is a division of two related numbers with the numerator being a subset of the denominator.
Incidence 
Prevalence
Period prevalence
Mean lifetime
Cumulative incidence
Trends 
Point prevalence
Median