Point Prevalence is defined as-

Ans. is 'd' i.e., Number of total cases at a given point of time * Prevalence refers specifically to all current cases (old and new) existing at a given point in time or over a period of time in a given population.* Prevalence is of two types: (i) Point prevalence, and (ii) Period prevalencei) Point prevalence# Point prevalence is defined as the number of all current cases (old and new) of a disease at one point of time, in relation to a defined population.Point prevalence =No. of all current cases (old & new) of a specified disease existing at a given in time------------------------------------Estimated population at same point in timex 100# When the term prevalence rate is used, without any further qualification it is taken to mean "point prevalence"ii) Period prevalence# It measures the frequency of all current cases (old 8c new) existing during a defined period of time (e.g. annual prevalence) expressed in relation to a defined population.# It includes cases arising before but extending into or through to the year as well as those cases arising during the year.Period prevalence =No. of existing cases (old 8c new) of a specified disease during a given period oftime interval------------------------------------------Estimated - mid - interval population at riskx 100* Prevalence is a proportion.* Prevalence is determined by cross sectional study.