29 Questions
What type of variable is a county of residence in epidemiology?
Nominal-scale variable
What is the definition of health according to the World Health Organization (WHO) in 1948?
A state of complete physical, mental, and social well-being
What is the term for the progression of a disease process in an individual over time, in the absence of treatment?
Natural history of disease
What is the main difference between a ratio and a proportion in epidemiology?
A ratio is a comparison of two quantities, while a proportion is a part of a whole
What is the term for the condition of being diseased?
Morbidity
What is the main characteristic of nominal-scale variables in epidemiology?
They have no numerical ranking
What is the primary characteristic of a ratio-scale variable?
It has a true zero point and is measured on a scale of equally spaced units
What is the purpose of the numerator in a frequency measure?
To provide the upper portion of a fraction
What is the distinguishing feature of a nominal variable with two categories?
It has mutually exclusive categories
What is the term for the relative magnitude of two quantities or a comparison of any two values?
Ratio
What is the characteristic of an interval-scale variable that distinguishes it from a ratio-scale variable?
It lacks a true zero point
What is the term for the spread of a distribution, as revealed by a graph?
Spread
What is the secondary attack rate among family contacts of cases?
20%
What is the relation between prevalence and incidence in a steady-state?
Incidence equals prevalence
What is the main purpose of measuring prevalence in a community?
To measure the burden of disease in a community
Why is it crucial to have correct interpretations in epidemiology?
To ensure accurate calculations and conclusions
How many decimal places should final answers have in epidemiological calculations?
2 decimal places
What is the percentage of people who became ill with diarrhea among those who ate cantaloupe at the Lansing picnic?
80%
What is the term for the person who gets the disease from eating contaminated food, for example, egg salad?
Primary case
What is the formula for calculating the primary attack rate?
Number of new cases / Population at risk * 100
In the example of the hepatitis A outbreak, what is the total number of persons in the 7 affected families?
32
What is the term for the percentage of people who become ill among those who were exposed to a primary case?
Secondary attack rate
What is the percentage of people who became ill with hepatitis A among the children attending the child care center?
10%
What is a characteristic of a proportion in measures of risk frequency?
It is a type of ratio in which the numerator is included in the denominator
What is the difference between a proportion and a rate in measures of risk frequency?
A proportion is a measure of the frequency with which an event occurs in a defined population, while a rate is a measure of the frequency with which an event occurs in a defined population over a specified period of time
What is the formula for calculating a proportion in measures of risk frequency?
Number of persons or events with a particular characteristic / Total number of persons or events, of which the numerator is a subset × 10 n
What is the term for the number of cases or events occurring during a given time period in measures of risk frequency?
Numerator
What is the term for the total number of persons or events, of which the numerator is a subset in measures of risk frequency?
Denominator
What is the difference between a prevalence rate and an incidence rate in measures of risk frequency?
A prevalence rate is a measure of the total number of cases of a disease or condition in a population at a given time, while an incidence rate is a measure of the number of new cases of a disease or condition in a population over a specified period of time
Study Notes
Measurement of Morbidity
- Morbidity is the condition of being diseased.
- Health is a state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity (WHO, 1948).
Types of Data
- Data can be Numeric or Descriptive.
- Nominal-scale variables have values that are categories without any numerical ranking, such as county of residence.
- Ordinal-scale variables have values that can be ranked but are not necessarily evenly spaced, such as stage of cancer.
- Interval-scale variables are measured on a scale of equally spaced units, but without a true zero point, such as date of birth.
- Ratio-scale variables are interval variables with a true zero point, such as height in centimeters or duration of illness.
Frequency Distributions
- Frequency distributions have three features: central location, spread, and shape.
- A quick look at a graph reveals these features.
Measures of Risk Frequency Measures
- Ratio: a comparison of two quantities, where the numerator and denominator need not be related.
- Numerator: upper portion of a fraction.
- Denominator: lower portion of a fraction.
- Example: 32-7 = 25, so 5/25*100 = 20%.
Incidence and Prevalence
- Incidence: a measure of risk, or the number of new cases occurring in a population over a specified period of time.
- Prevalence: a measure of the burden of disease in a community, or the number of people with a disease living in a community.
- When there is a steady-state, prevalence and incidence are related.
- Prevalence increases with successful programs, but may give the appearance of failure.
Measures of Risk Frequency Measures
- Proportion: a comparison of a part to the whole, often expressed as a decimal, fraction, or percentage.
- Rate: a measure of the frequency with which an event occurs in a defined population over a specified period of time, often a proportion with an added dimension of time.
- Examples: attack rate, incidence rate, prevalence rate.
Examples of Morbidity Frequency Measures
- Attack Rate: measures the number of people who become ill after exposure to a risk factor.
- Incidence Rate: measures the number of new cases of a disease occurring in a population over a specified period of time.
- Prevalence Rate: measures the number of people with a disease living in a community at a specific point in time.
- Prevalence: measures the number of people with a disease living in a community over a specified period of time.
Test your understanding of epidemiologic data, including types of data, ratio, proportion, and rate. Learn how to describe data according to person, place, and time, and calculate incidence and prevalence rates. This quiz is based on a lecture from the Applied Nutrition Department on Nutritional Epidemiology and Research Methods.
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