A key aspect of epidemiology is surveillance studies, which provides the numerical data and statistics that epidemiologists use. Surveillance studies are done systematically to monitor the health of populations and helps with identifying any new health problems or disease that may develop, as well as evaluating the effectiveness of existing health intervention measures in place. These studies also rely on TPP to collect data and presents it in simple graphs and tables which are easy to summarize and understand. These studies are especially important in helping guide policy making decisions and helping epidemiologists understand which interventions work and which don't. It is also important for donors as they rely on surveillance data to analyze the usefulness of their investments and whether it is being used effectively or not.