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BHS210 M2C- Measures of Morbidity and Mortality
Twenty-five children in Fallsburg Elementary School (with a population of 60 pupils) received their immunization against whooping cough to protect the school’s student population. In your role as health officer, you collected the documentation from parents on the first day of school. You found that 25 students had received their immunization against the disease. You have been asked to explain some basic epidemiologic concepts to the parents who did not have their children immunized.
You have been tasked to do the following:
1. Define the term population at risk and indicate which of the elementary students are not at risk.
2. Also describe the difference between incidence and prevalence.
Centers for Disease Control and Prevention (CDC). (2012). Lesson three: Measures of risk. Principles of epidemiology in public health practice (pp. 3-20:3-23). U.S. Department of Health and Human Services, Office of Workforce and Career Development. https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section6.html
Centers for Disease Control and Prevention (CDC). (2019). Ten leading causes of death and injury 2017. https://www.cdc.gov/injury/wisqars/LeadingCauses.html
New York Department of Health. (n.d.). Basic statistics: About incidence, prevalence, morbidity, and mortality. Retrieved from www.health.ny.gov/diseases/chronic/basicstat.htm
Harvard Kennedy School’s Shorenstein Center and the Carnegie-Knight Initiative (n.d.). Statistical terms used in research studies: A primer for media. https://journalistsresource.org/tip-sheets/research/statistics-for-journalists/
What is “population at risk”?
The population at risk refers to individuals who are specifically capable of coming down with the condition, or developing the condition of interest. For example, we can give several good examples for many infectious diseases, if there is a specific immunization against that disease to protect the population, and then the individuals who have received the immunization generally will not be part of the population at risk.
What is morbidity?
The term morbidity refers to sickness in the population. For example, people who are afflicted with certain diseases and conditions. An example would be people who are afflicted with diabetes, Type II Diabetes, or people who are afflicted with the flu at any given time.
What is mortality?
Mortality refers to death and it is an important outcome variable that is used in epidemiologic studies. Death is noted in important data sources such as death certificates.
What is incidence?
Incidence is a measure of disease that allows us to determine the probability of a person being diagnosed with a disease during a given period of time. Therefore, incidence is the number of newly diagnosed cases of a disease. An incidence rate is the number of new cases of a disease divided by the number of persons at risk for the disease.
Example: If in one year, five women are diagnosed with breast cancer, out of a total female study population of 200 (who do not have breast cancer at the beginning of the study period), then the incidence of breast cancer in this population is 0.025 (i.e. 5 ÷ 200 = 0.025)
What is prevalence?
Prevalence is a measure of disease that allows us to determine the likelihood of a person having a disease. Therefore, the number of prevalent cases is the total number of cases of disease existing in a population. A prevalence rate is the total number of cases of a disease existing in a population divided by the total population.
Example: If 1,200 people were recently diagnosed with lung cancer and 3,500 are living with lung cancer in a population of 40,000 people, then the prevalence of cancer is 0.118. (1,200 + 3,500 ÷ 40.000 = 0.1175 rounded to 0.118)
The likelihood that a person belonging to a particular group, categorized according to age or some other factor such as occupation, will suffer a disease, illness, injury, or sickness.
A mortality rate is the amount of deaths in a given population during a given period of time. The rate is commonly expressed in deaths out of 100 or 1000 individuals. For instance, if in a town of 10,000 inhabitants, 10 people die of the flu, the flu mortality rate would be 1 in 1000. Mortality rates can be based on simply how many die of any cause in a population, or can be used to describe the death rate of a certain illness or condition.
Mortality rates have many uses, but are often utilized to describe the increase or decrease in a cause of death over a lengthy time period. Looking at the mortality rates over time can help health officials understand where to focus prevention and safety efforts, and indicate possible trends in death due to factors affecting the population.
Example: Infant mortality rate – It is the number of children dying under a year of age divided by the number of live births that year.
Example: 1,300 infant deaths in 2009 in a State; 150,000 live births in 2009 in that state. Therefore, the Infant Mortality Rate is:
1,300 ÷ 150,000 x 1,000 = 8.7 infant deaths per 1,000 live births in 2009 in that state.