Epidemiology is defined as the study of the distribution and determinants of health and disease in human populations. Basically, this all boils down to the fact that epidemiology is population-based. Epidemiology is increasingly important in medicine and population well-being. Insights generated by epidemiology over the past half century have led to the development of a number of specific public health measures designed to improve population health. Epidemiology is the basic science of both preventative medicine and evidence-based practice, and as such is becoming an indispensable tool for physicians in general and family physicians in particular. The epidemiologist attempts to place clinical or other observations in the context of the population. Unlike mortality, morbidity is not a single, unambiguous biological state but a gradient or spectrum of disease from asymptomatic conditions or risk factors through symptoms of varying severity, up to profound disability. Morbidity measures the incidence or prevalence of acute and chronic diseases, depending on the cause. Measuring morbidity is relatively simple if all cases present to the National Health Service. Among morbidity measures, two that are particularly useful to policy makers and health care purchasers are causes of health care spending. The leading cause of healthcare spending includes injuries, severe depression, arthritis and chronic diseases of major organs, including the heart. The number or rate of nonfatal outcomes is not used as often as mortality in assessing disease burden. The only chronic noninfectious condition for which the United States has national data on incident cases is cancer (Scutchfield & Keck, 2003). Hospitalization rates are sometimes used to estimate the burden of disease in a population. Hospitalization rates have the advantage of being relatively easy to obtain and are useful for some analyses, but they are distorted indicators of burden for most conditions. For example, the increasing use of outpatient care for conditions that previously required hospitalization may substantially influence the usefulness of these data for assessing burden. In the United States, heart disease is the leading cause of hospitalization, followed in order by childbirth, psychosis, pneumonia, cancer, and fractures (Thacker SB, Stroup DF, Carande-Kulis V, Marks JS, Roy K, Gerberding JL, 2006). Patients with fractured femurs or acute schizophrenia, for example, fall into this category because the severity of their clinical condition almost always requires hospitalization (Scutchfield & Keck,