Measures of Disease Frequency

What are the four components for measuring disease frequency?

1. Population

2. Cases of disease

3. Size of population

4. Time

What are the two types of populations?

1. Fixed population: defined by event, is permanent

   1. Ex: People born in a certain year

2. Dynamic population: defined by a state or condition

   1. Ex: Residents in Vancouver

Define Cases of disease and Size of population as numerator / denominator

Cases of disease is the numerator

Size of population is the denominator

What are the three types of measures for Disease Frequency?

1. Ratio: compares two quantities

2. Proportion: measures a sub-group in a group

3. Rate: measures time in the denominator

Give an example for ratio

A hospital has 20 male patients and 10 female patients

• Ratio: 2:1

Give an example for proportion

Out of 100 patients, 20 have asthma

• Proportion: 20% of patients have asthma

Give an example for rate

10 people develop an infection over 500 years

• Rate: 0.02 cases per person-year

What are the three types of epidemiological measures?

1. Prevalence

2. Cumulative Incidence

3. Incidence rate

What does prevalence measure during when?

Prevalence measures existing cases of disease in a population during a specific time period

What is Point Prevalence?

Point Prevalence is the proportion of the population that has the disease at a single point of time

What is the prevalence formula? Are there units?

No Units, but time period must be stated in the answer

Use the prevalence formula for this example. Provide an interpretation at the end.

What does incidence measure? What does it involve?

Incidence measures new cases of a disease in a population during a specific time period

• Involves the transition from one state to another

When would you use prevalence vs. incidence for disease?

Prevalence would be used for an existing disease, while incidence would be used for a new disease