Properly identifying and understanding outliers is an important step in analyzing descriptive data. Cases at the very beginning or end of an outbreak are the most obvious outliers, but investigator should also pay close attention to any observations that vary so widely from the rest of the data that they seem to be in error or to have come from a different population. The first thing that investigator should do when considering outlier is to make sure they are not mistakes due to data collection, coding, or entry error. For example, if there is only one 1-year-old patient or one 95-year-old patient, and the remain case patients range in age from 10 to 60 years old, investigators should confirm that the outlying values for age have been accurately recorded or calculated and entered into the database.