Investigation 3-5
Reversed Time Order

Synopsis

Students explore the fourth of five possible explanations for finding an association: reversed time order, in which the suspected outcome actually came before the exposure.  Students consider what the four basic epidemiologic study designs can tell them about the time order of an exposure and an outcome.  Students review the results of a cross-sectional study that found an association between playing violent video games and aggressive behavior.  They realize that, given the study design, it is possible that the association was found because aggressive people like to play violent video games, and not because playing violent video games causes aggressive behavior.  Students continue to learn that causation is only one explanation for finding an association between an exposure and an outcome; that because observational studies are flawed, other explanations must also be considered, including reversed time order.

Investigation Preparation Checklist

Check alignment with standards.

National or State file

Review Epidemiology Background for Module 3.

Word or PDF file

Review teacher's notes and slides:  [en espaņol:]

Copy Investigation 3-5: Epi Log Worksheet for each student.  [en espaņol:]

Word or PDF file

Estimated Time / Time Management

Approximately one class period. Time can be managed by increasing or decreasing the number of examples students give of associations between an exposure and an outcome for which the time order might be reversed.

Look For Students To:

	Explain how an association is found by making and comparing rates.
	Explain why association is not synonymous with causation.
	Provide specific examples, other than causality, for an association.
	Describe an association between an exposure and an outcome for which the time order might be incorrect.
	Understand what study designs are best at identifying the time order of an exposure and an outcome.
	Understand what study designs do not identify the time order of the exposure and the outcome.