The first step involves the rather mechanical task of amassing all the facts about a situation or problem. The second is the more contemplative step of conceiving a plausible explanation for why the situation exists. This second phase, known as hypothesis formulation, involves examining all the facts and asking questions from different perspectives. It is the bridge between descriptive and analytic epidemiology. But before testing a hypothesis, researchers must describe the problem in standard terms.
Prevalence reveals how many cases exist in a population at a given time.
The incidence rate records the rate at which new cases are appearing within that population over a specific period. Knowing the magnitude of disease or injury is only the beginning of the epidemiologist's work. Specifying person, place, and time is crucial for identifying risk groups, narrowing the search for risk factors, and targeting and evaluating interventions. People may be identified by sociodemographic characteristics that promote or inhibit susceptibility to disease or injury. They may also be identified by habits or lifestyles that influence the likelihood of harmful or beneficial exposures.