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Concrete Example
It is important to not get confused about Point Prevalence and Point Prevalence. In this concrete example from the Center for Disease Control (https://www.cdc.gov/OPHSS/CSELS/DSEPD/SS1978/Lesson3/Section2.html#TXT31), it shows the difference between the two. In the figure below, there are 10 new cases of disease from October 1, 2004 to September 30, 2005. The total population is 20. Each horizontal line represents one person, and the length of the line represents the duration of the disease. The down arrow (↓) indicates the date of onset of disease. The up arrow (↑) represents date of recovery, and the cross (×) represent the date of date of death.

The Point Prevalence on April 1, 2005 is the number of people who have the disease on the date divided by the population on that date. On April 1, seven people (persons 1, 4, 5, 7, 9, and 10) had the disease, and two people had died (persons 2 and 8). Therefore, the Point Prevalence $$  = \frac{7}{18} \times 100\% = 38.89\%$$.

Moving on to the Period Prevalence from October 1, 2004 to September 30, 2005. The numerator of Period Prevalence is all the people with the disease any time during the period, and the denominator is the total population. In this example, the first 10 people had the disease during the period, and the total population is 20. Therefore, the Period Prevalence $$ = \frac{10}{20} \times 100\% = 50\%$$.

Properties and Uses of Prevalence Measures
Prevalence and Incidence are very similar, and people oftentimes get confused of the two. The main difference exists in their numerators. The numerator of Prevalence include all people who have a certain disease during a specific period of time, regardless of when the onsite of the disease is. In other words, it includes the people who have existing disease as well as newly developed disease. But the numerator of Incidence only includes the people who develop the disease during the specific period of time.

$$ Prevalence \ Numerator = ALL\ cases\ present\ during\ a\ given\ time\ period $$ $$ Incidence \ Numerator = NEW\ cases\ occurred\ during\ a\ given\ time\ period $$

Given the properties of Prevalence, it is used mainly to measure diseases which have long duration, and the dates of the onside that are difficult to pinpoints. For example, Prevalence is used to measure chronic diseases such as diabetes or osteoarthritis. However, prevalence is not so useful when measuring diseases that are easily transmitted but with short duration. For those diseases, such as chickenpox, Incidence would be a better measurement.