Prevalence research designs aim to determine, objectively, the prevalence of opinions or beliefs (subjective reality) or experiences (objective reality) in a specific population. It is focused on one variable at a time, a variable that has been identified and operationally defined in advance. Prevalence studies require a representative sample in order to generalize to the population of interest. They typically rely on archival records or questionnaires for measurement. Results are numerical, and require some understanding of rates, averages, variability, and confidence intervals. Prevalence research contributes to HDFS by providing accurate counts of the issues that we study.