The director of a community health organization reads that about 1,300 new cases of HIV infection are expected in her city in the coming year. This statement illustrates an epidemiological statistic called significance or prevalence (is a sample of a population who have a specific characteristic in a given period). Just randomly select a sample from the population you want to describe. It is the number of people in the sample with the characteristic of interest, divided by the total number of people in the same sample (differences in methodology may impact significance/prevalence estimates).