CLIO Learning Modules
Study DesignSelectionSample SizeData Collection and AnalysisHuman Subjects

Modules
Hypothesis
'Me too studies'
Target Population
Exposure
Outcome
Rate
Experiment
Attributable Risk
Relative Risk
Data Sources
Study Time
Case Control
Nested Case-Control
Prospective Cohort
Retrospective Cohort
Randomized Clinical Trial
Exposure
Definition

The exposure is the independent factor of interest in your study — what you think causes the outcome.

Explanation

The most basic form of the hypothesis is: X causes Y, where X is the exposure.
Example: Smoking causes cancer. Smoking is the exposure.

Examples

(exposures are in italics)

Your exposure should not be a result of the outcome.
Example: Red spots cause chickenpox.
Red spots are a direct result of chickenpox infection.
Reformulated: Chickenpox causes red spots.

Exposure and outcome are relative.
Example: HIV causes AIDS.
There is nothing wrong with this example. However, it is important to remember that one study’s exposure is another’s outcome.
Example 2: Unsafe sex can cause acquisition of HIV.

Your exposure must be measurable.
Example: Having a bad attitude causes wrinkles.
How do you plan to measure having a bad attitude?
Reformulated: Daily frowning causes wrinkles.

Expansion

The exposure does not need to be a true etiologic cause — they are often markers for other processes or conditions. For example, suppose that you are studying the association between demographics and outcomes following myocardial infarction. Income may be included as a risk factor in your study, and treated as an exposure in the analysis. The absence of money itself does not lead to poor outcomes, but rather serves as a marker for other factors that may be more difficult to measure such as access to health care.


June 4, 2004 v0.20
Copyright © 2004 Stanford School of Medicine