Point and Period Prevalence

Period and Point Prevalence

Prevalence data and is important in describing the health burden of a population and helps in estimation of frequency of an exposure, and in prioritization and allocation of health resources - facilities and personnel. There are two types of prevalence - period prevalence and point prevalence. Period prevalence refers to the total number of cases of a disease that exist during a specified period of time, for example a week, a month or even a longer time interval (Szklo & Nieto, 2007). To arrive at period prevalence, one must combine the number of cases observed at the beginning of the interval - point prevalence - with the new cases that occur during the interval. In essence, for period prevalence, cases are counted even if they die, migrate to new location, or even recur as episodes during the period of study. As such, period prevalence is calculated as the number of cases ill over the average population during a given time period. For example, if an epidemiologist asked women in Kibera estate whether they have been diagnosed as having any form of cancer, other than ovarian; such a question does not ask about a current disease but rather seeks to access the lifetime history. Thus, in this case, it refers to a period prevalence in which the period is now the entire life span. To calculate the period prevalence, the epidemiologist need to know the average population of the estate (say 50,000) and the number of the women who responded yes to the question (assume 1,508). Therefore, the period prevalence of other types of cancer other than ovarian in the study population was 1, 508/50,000 which is 3.01%.

On the other hand, point prevalence refers to the number of cases at a point in time. In essence, it's a measure of the proportion of the population with a given disease or physiological condition at that very particular time such as on a given date (Szklo & Nieto, 2007). This measure is mainly used to describe occurrence of some chronic conditions. As such, it is calculated by dividing the number of observed cases on a particular date over the number of people in the population as on that date. Also, when the time period is not specified, the prevalence usually implies a particular point in time hence point prevalence. For example, the prevalence of diarrhoea in Daadab refugees camp on May 12th, 2012 was found to be 21% or the prevalence of obesity among children aged 12 to