Lecture 16: Measuring Disease Occurrence Flashcards
What are populations?
2
- A group of people in a geographical area
- A group of people with a common characteristic
What is first used to understand a disease in a population?
Measuring a diseases occurance
Why is the occurrence of disease measured in populations?
3
- To understand health status
- Trends in disease over time
- How disease impacts different groups
What are the measures of disease occurrence?
3
- Prevalence
- Incident proportion
- Incident rate
What is incident proportion sometimes referred to?
Cumulative incidence
What is prevalence?
The proportion of a population who HAVE the disease at a point in time
What does prevalence tell us?
The proportion of a population who have a disease at a certain point in time
Why do you want to consider the prevalence of a disease in a population?
To understand the burden of the disease and how to allocate resources
How do you calculate prevalence?
Number of people with the disease at a given point in time
/
Total number of people in the population at that point in time
When reporting prevalence what aspects must be expressed to interoperate findings?
(5)
- Measure of occurrence
- Exposure or outcome
- Population
- Time point
- Value
What are 2 limitations of prevalence?
- Difficult to assess the development of disease
- It is influenced by the duration of the disease
How does duration influence prevalence?
At a given time the prevalence can be higher due to cases lasting longer with out there being an actual higher amount of cases throughout the study
What is incidence?
The occurrence of NEW CASES of an outcome in a population during a specific period of follow-up
What is incidence proportion?
The proportion of an outcome-free population that develops the outcome of interest in a specific time period
How do you calculate incidence proportion?
Number of people who develop the disease in a specified period
/
Number of people at risk of developing the disease at the start of the period
What are reasons people are not considered to be at risk at the start of a study?
(2)
- They already have the condition
- The condition is something that they cannot develop
When reporting incidence proportion what aspects must be expressed to interoperate findings?
(5)
- Measure of occurrence
- Exposure or outcome
- Population
- Time point
- Value
Why is incident proportion used?
It shows the average risk amongst a population, but not of each individual
What are limitations of incidence proportion?
2
- Assumes a ‘closed’ population (does not account for people coming or going in populations)
- Highly dependent on the time period (longer time period = higher incidence proportion)
What is incidence rate?
The rate at which new cases of the outcome of interest occur in a population
How do you calculate incidence rate?
Number of people who develop the disease in a specified period
/
Number of person-years at risk of developing the disease
What are person-years at risk of developing a disease?
The sum of everyone in the population’s time at risk of becoming a case
Why might someone stop being at risk of disease?
- They become a case
- They are lost to follow-up
- Follow-up time ends
When reporting incidence rate what aspects must be expressed to interoperate findings?
(4)
- Measure of occurrence
- Exposure or outcome
- Population
- Value
What are limitations of incidence rate?
Information needed to calculate is often difficult to attain and complex to calculate
What does prevalence approximate?
Incidence X average disease duration
What ca changes to incidence and duration alter?
Disease prevalence
When comparing populations can disease be affected by age?
Yes
When comparing populations do age structures often differ?
Yes
What does age standardisation do?
Removes the effects of populations having different age structures
When is age standardisation used?
When age structures differ in each population and disease risks vary by age
