Chapter 3: Epidemiologic Measurements

Vocabulary and formulas for epidemiologic measurements including mortality and natality rates derived from Chapter 3's lecture notes.

Ratio

The value obtained by dividing one quantity by another.

Proportion

A type of ratio in which the numerator is part of the denominator, which may be expressed as a percentage.

Percentage

A proportion that has been multiplied by 100, following the formula $\frac{A}{A + B} \times 100$.

Rate

A type of ratio that differs from a proportion because the denominator involves a measure of time ($t$).

Count

The number of cases of a disease or other health phenomenon being studied, where reports of single cases can have public health significance.

Incidence

The occurrence of new disease or mortality within a defined period of observation in a specified population.

Cumulative Incidence (Incidence Proportion)

$$\frac{\text{Number of new cases over a time period}}{\text{Total population at risk at the start of the same time period}}$$

Incidence Rate

$$\frac{\text{Number of new cases over a time period}}{\text{Total time each person was in the population at risk}} \times \text{multiplier}$$

Population at Risk

Members of the population who are capable of developing the disease or condition being studied.

Prevalence

The number of existing cases of a disease, health condition, or deaths in a population at some designated time.

Point Prevalence

All cases of a disease or health condition that exist at a particular point in time relative to a specific population.

Period Prevalence

All cases of a disease or health condition within a specific period of time, such as the past 12 months.

Lifetime Prevalence

Cases of disease or health condition diagnosed at any time during the person’s lifetime.

Burden of Disease

Terms used to describe the scope or amount of disease in a population.

Life Expectancy

The number of additional years that a person is expected to live at any particular age, such as at birth.

Crude Mortality Rate

A rate that has not been modified to account for demographic factors and is calculated as $\frac{\text{Number of deaths from all causes over a specified period}}{\text{Total population size}} \times 100,000$.

Reference Population

The population from which cases of a disease have been taken or the population within which the deaths occurred.

Case Fatality Rate (CFR)

The percentage of deaths due to a disease among persons who are afflicted with that disease, calculated as $\frac{\text{Number of deaths due to disease}}{\text{Number of cases of disease}} \times 100$.

Proportional Mortality Ratio (PMR%)

$$\frac{\text{Number of deaths due to a specific cause}}{\text{Total number of deaths in the population}} \times 100$$

Cause-Specific Mortality Rate

$$\frac{\text{Mortality from a specific cause}}{\text{Population size at midpoint of time period}} \times 100,000$$

Age-Specific Mortality Rate

The number of deaths in a specific age group of a population during a specified time period.

Sex-Specific Mortality Rate

$$\frac{\text{Number of deaths in a sex group}}{\text{Total number of persons within that sex group}} \times \text{multiplier}$$

Direct Age Adjustment

A procedure that uses age-specific mortality rates for a population of interest and applies them to a standard population with a known age structure.

Indirect Age Adjustment

A procedure used to adjust mortality rates based on the number of observed deaths in a population over a period of time.

Natality

The birth rate.

Maternal Mortality Rate

The number of maternal deaths resulting from pregnancy-associated causes per 100,000 live births.

Infant Mortality Rate

$$\frac{\text{Number of infant deaths (0–365 days)}}{\text{Number of live births in the same year}} \times 1,000\,\text{live births}$$

Neonatal Mortality Rate

$$\frac{\text{Number of infant deaths under 28 days}}{\text{Number of live births during a year}}$$

Fetal Death Rate

$$\frac{\text{Number of fetal deaths after 20 weeks or more gestation}}{\text{Number of live births + number of fetal deaths after 20 weeks or more}} \times 1,000$$

Late Fetal Death Rate

$$\frac{\text{Number of fetal deaths after 28 weeks or more gestation}}{\text{Number of live births + number of fetal deaths after 28 weeks or more}} \times 1,000$$

Crude Birth Rate

$$\frac{\text{Number of live births during a year}}{\text{Resident population at midpoint of the year}} \times 1,000$$

General Fertility Rate

$$\frac{\text{Number of live births during a time interval}}{\text{Number of women age 15–44 years in the area}} \times 1,000$$