Morbidity Versus Mortality: What's The Difference?

Morbidity and mortality are two terms that are frequently used in the area of epidemiology. Epidemiology refers to the study of what causes health diseases and outcomes among populations, including the spread and determinants of those health issues, according to the Centers for Disease Control and Prevention (CDC).

Morbidity and mortality are two concepts within epidemiology to measure the progression and intensity of an adverse health event (per StatPearls). They can also be used to determine the effectiveness of interventions and health care systems. Ultimately, morbidity and mortality are important in helping epidemiologists figure out how a health event will affect the population.

The two terms can get confused with each other, but while they are similar, they are not the same. Morbidity is when you have an illness or condition. Sometimes this refers to an acute condition, but often it refers to a chronic (long-lasting) condition such as heart disease, according to Healthline

Within morbidity statistics are two subcategories of data called incidence and prevalence. Incidence determines the probability of someone contracting a specific illness over a length of time, explains the New York State Department of Health. Thus, it refers to the number of people newly diagnosed with a disease. Prevalence refers to how many people have the disease in a population, and therefore includes both new and existing cases.

Mortality is the number of deaths from an illness

For most people, mortality is easier to understand because they have heard the term before. Mortality describes the number of deaths that have resulted from a specific condition and is often referred to as the "mortality rate", explains Healthline.

When epidemiologists figure out the mortality rate, they take the number of deaths over a length of time in a specific population. For example, based on data from 2013 to 2017, cancer causes 158.3 deaths per 100,000 men and women every year in the United States, according to the National Cancer Institute. The number is calculated by taking the number of deaths within a period of time and dividing it by the total population, per National Center for Biotechnology Information.

The leading causes of death in the United States include stroke, chronic lower respiratory diseases, unintentional injuries, cancer, and heart disease, according to the CDC.