Epidemiology Measures of Morbidity and Mortality

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Questions and Answers

What are the main measures of morbidity in epidemiology?

Incidence Rate, Attack Rate, Prevalence

What does the incidence rate measure?

The number of new cases of a disease (or other health-related phenomenon) that occur during a specified period of time in a population at risk.

What is the formula for calculating the incidence rate?

Incidence rate = (new cases occurring during a given time period / population at risk during the same time period) x 10^n

The numerator for the incidence rate should include cases which occurred earlier.

False Signup and view all the answers

The denominator for the incidence rate should include persons with the disease.

False Signup and view all the answers

What is the incidence rate from October 1, 1990 to September 30, 1991, based on the timeline provided?

4/14 Signup and view all the answers

What factors can affect the incidence rate?

New risk factors, changing habits, changing virulence of causative organisms, changing of intervention programmes, selective migration of susceptible persons, population pattern, reporting, screening, and new diagnostic tools. Signup and view all the answers

What does the attack rate measure?

The number of new cases among the population during a specific period, typically during an outbreak. Signup and view all the answers

What is the formula for calculating the attack rate?

Attack rate = (Number of new cases among the population during the period / Population at risk at the beginning of the period) x 100 Signup and view all the answers

What is the attack rate of gastroenteritis if 46 out of 76 people who attended a picnic developed gastroenteritis?

61% Signup and view all the answers

What does the prevalence rate measure?

The number of cases (new and old) of a disease (or other health-related phenomenon) at a given point or period in time. Signup and view all the answers

What is the formula for calculating the prevalence rate?

Prevalence = (all new and pre-existing cases during a given time period / population during the same time period) x 10^n Signup and view all the answers

What is the difference between point prevalence and period prevalence?

Point prevalence measures the number of cases at a specific point in time, while period prevalence measures the number of cases over a specified period. Signup and view all the answers

The numerator for prevalence includes all persons ill from a specified cause during a specified time interval, regardless of when the illness began.

True Signup and view all the answers

What is the point prevalence on April 1 based on the timeline provided?

7/18 Signup and view all the answers

What is the relationship between incidence and prevalence?

Prevalence is influenced by both incidence (the rate of new cases) and the duration of the disease. Signup and view all the answers

What factors may affect the prevalence rate?

Incidence, duration of the disease, selective migration, and disease treatments & outcome. Signup and view all the answers

What is the formula for calculating the annual mortality rate for all causes?

Annual mortality rate for all causes = (Total number of deaths from all causes in 1 year / No. of persons in the population at midyear) x 1,000 Signup and view all the answers

What is the formula for calculating the age-specific mortality rate for children younger than 10 years of age?

Annual mortality rate for children younger than 10 years of age = (No. of deaths from all causes in one year in children younger than 10 years of age / No. of children in the population younger than 10 years of age at midyear) x 1,000 Signup and view all the answers

What is the formula for calculating the cause-specific mortality rate?

Annual mortality rate from [specific cause] = (No. of deaths from [specific cause] in one year / No. of persons in the population at midyear) x 1,000 Signup and view all the answers

What is the formula for calculating the case-fatality rate?

Case-fatality rate = (No. of individuals dying during a specified period of time after disease onset or diagnosis / No. of individuals with the specified disease) x 100 Signup and view all the answers

What is proportional mortality?

It is the proportion of all deaths that are due to a particular cause for a specified population and period. Signup and view all the answers

Study Notes

Measures of Morbidity and Mortality

Morbidity rates indicate the extent of illness, injury, or disability in a defined population.
In epidemiology, the main measures of disease frequency are incidence rate, attack rate, and prevalence.
Epidemiologic research assumes disease occurrence is not random, systematic investigation of populations can identify causal and preventative factors, and comparisons are crucial for systematic investigations.

Learning Objectives

Students will be able to list the main measures of morbidity.
Students will be able to define and calculate morbidity rates.
Students will be able to recognize the relation between incidence and prevalence rates.
Students will be able to define and calculate mortality rates.

Incidence Rate

Incidence measures the number of new cases of a disease or other health-related phenomenon during a specific period in a population at risk.
Incidence rate = (new cases occurring during a given time period / population at risk during the same time period) x 10ⁿ
The numerator should only include new cases occurring during the specified period; earlier cases should not be included.
The numerator must come from the population at risk for developing the disease.
The denominator should include people at risk of developing the disease during the time period.
The denominator does not include individuals with the disease.
The denominator can change as people develop the disease.

Attack Rate

An attack rate is a variant of incidence rate, applied to a narrowly defined population observed for a limited time, such as during an epidemic.
Attack rate is usually expressed as a percentage.
Attack rate = (number of new cases among the population during the period / population at risk at the beginning of the period) x 100

Prevalence Rate

Prevalence measures the number of cases (new and old) of a disease or other health-related phenomenon at a point or period in time.
Prevalence = (all new and pre-existing cases during a given time period / population during the same time period) x 10ⁿ
The numerator includes all persons ill from a specified cause during a specific time interval.
The denominator includes the total population in the same place during the specified time interval.

Relation between Incidence and Prevalence

Prevalence = incidence x duration of disease
Higher incidence results in higher prevalence.
Longer duration of the disease results in higher prevalence.
Several factors may affect prevalence rate: incidence, duration of the disease, selective migration, and disease treatments and outcomes.

Interpretation of Trends

Rapid recovery from disease (e.g., new drug discovery)
Fatal disease (e.g., increased virulence)
Treatment failure or reduced effectiveness
Selective out-migration of cases

Mortality

Mortality risk or rate is an example of incidence where death is the outcome of interest.
The denominator includes both prevalent cases of the disease and individuals at risk of developing the disease.

Annual Mortality Rate

Annual mortality rate for all causes (per 1,000 population) = (Total no. of deaths from all causes in 1 year / No. of persons in the population at midyear) x 1,000

Cause-Specific Mortality Rate

Annual mortality rate from a specific cause (e.g., lung cancer) = (No. of deaths from the specific cause in one year / No. of people in the population at midyear) x 1,000

Case-fatality Rate

Case-fatality rate (percent) = (No. of individuals dying during a specified period after disease onset or diagnosis / No. of individuals with the specified disease) x 100

Proportional Mortality

Proportional mortality is the proportion of all deaths attributable to a specific cause during a particular time and place.

Other Factors and Examples

Charts and graphs depicting trends in morbidity and mortality rates are included for different diseases and populations.
Includes various specific examples of diseases and populations presented in different charts.
Age-specific mortality.

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Description

This quiz covers key concepts in epidemiology, focusing on measures of morbidity and mortality rates. Students will learn to define, calculate, and differentiate between incidence and prevalence rates. Discover the significance of these metrics in public health research and population studies.