researchers want to know CV risk about African American populations but do not have data for every person.If a researcher wanted to learn whether being certain ethnicity increase a risk of particular disease, it would not be practical to study every individual from that ethnicity . Instead, the researcher might select a sample of the population. A sample is a smaller group of members of a population selected to represent the population. In order to use statistics to learn things about the population, the sample must be random. A random sample is one in which every member of a population has an equal chance of being selected. The most commonly used sample is a simple random sample. It requires that every possible sample of the selected size has an equal chance of being used.