Lecture 18: Measures of Association Flashcards
What is the importance of a comparison group in analytic epidemiology?
To have a baseline of the outcome because we need to see whether the exposure is associated with the outcome (ie. does the exposure increase or decrease the likelihood of the outcome).
How can we find associations?
through analytic study designs
What are five examples of analytic study designs?
- cross sectional
- ecological
- cohort
- case-control
- RCTs
Fundamental characteristics and logic of analytic study designs can be described using _______ and _______
PECOT
GATE
What does PECOT stand for?
Population Exposure Comparison Outcome Time
What is meant by the “population” of analytic study designs?
the group of people in the study
What is meant by the “exposure” of analytic study designs?
what the potential determinant is
What is meant by the “comparison” of analytic study designs?
what the potential determinant is being compared to
What is meant by the “outcome” of analytic study designs?
the health outcome being assessed
What is meant by the “time” of analytic study designs?
how long people are being followed up for
In the GATE frame, what is the difference between the source and the sample?
The source is the population which the sample is recruited from whereas the sample is the population included in the study
What are two measures of association that we can measure?
relative risk
risk difference
How can you calculate relative risk?
incidence of the exposed group divided by the incidence of the comparison group
What does the relative risk show?
how many times as likely is the exposed group to develop the outcome than the comparison
What is the null value for relative risk and how does this come about?
1
when the incidence in the exposed and comparison groups are the same so there is no association between the exposure and the outcome
What does it mean if the relative risk is greater than the null value?
There is a greater incidence of outcome in the exposed group compared to the comparison group and therefore there is a greater likelihood of the outcome in the exposed group
What does it mean if the relative risk is less than the null value?
There is a greater incidence of outcome in the comparison group compared to the outcome group and therefore there is a greater likelihood of the outcome in the comparison group
What is the template for interpreting relative risk?
The [exposed group] were [value] as likely to develop [outcome] compared to [comparison]
How can you calculate risk difference?
incidence in the exposed group minus the incidence in the control group
What does the risk difference show?
How many extra/fewer cases of the outcome in the exposed group are attributable to the exposure
What is the null value for risk difference and what does this mean?
0
This means that there is no difference in the incidence of the outcome of interest between the exposed and comparison group
If the risk difference is greater than the null value, is the exposure a risk or protective factor?
risk
If the risk difference is smaller than the null value, is the exposure a risk or protective factor?
protective
What is the template for interpreting risk difference?
What is different about reporting incidence rate and incidence proportion?
There were [value] extra/fewer cases of [outcome] in [exposed group] compared [comparison group].
For the value in incidence proportion, you would say there were ___ extra/fewer cases per 100 people over ____ years whereas for incidence rate, you would say something like there were _____ extra/fewer cases per 100 person years
What are the benefits of using relative risk as the measure of association?
it gives clues to the causes and shows the strength of the association
What are the benefits of risk difference?
it shows the impact of the exposure and removing the exposure
