IS COMPARISON OF THE PREVALENCE OF DISEASE APPROPRIATE AS HEALTH INDICATOR BETWEEN TWO POPULATIONS? comparing the number of people found to have the condition within the total number of people studied, and is usually expressed as a fraction, as a percentage or as the number of cases per 10,000 or 100,000 people. Point prevalence is the proportion of a population that has the condition at a specific point in time. Period prevalence is the proportion of a population that has the condition at some time during a given period, and includes people who already have the condition at the beginning of the study period as well as those who acquire it during that period. Lifetime prevalence (LTP) is the proportion of a population that at some point in their life (up to the time of assessment) have experienced the condition (2), or simply, the prevalence of a disease is the proportion of people with a given disease at a given time. Prevalence is conventionally expressed as the proportion or percentage of cases in a given population at