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PUBHLTH 101 (20)

David Timberlake (20)

Lecture 12

Department

Public HealthCourse Code

PUBHLTH 101Professor

David TimberlakeLecture

12This

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ABSOLUTE RISK: incidence rate does NOT indicate whether the exposure is associated with an

increased risk of the disease

• To address the question of association, we must use approaches that involve explicit

comparisons

• Association between a certain exposure & outcome: to measure whether there is an excess

risk of the disease in persons who have been exposed to a certain agent

• Possible because participants are randomly assigned/allocated

INTERPRETING THE RELATIVE RISK

RR = 1 Risk in exposed equal to risk in non exposed (no association)

RR > 1 Risk in exposed greater than risk in non exposed (positive association; possible causal

association)

RR < 1 Risk in exposed less than risk in non exposed (negative association; possible protective

association)

Odds Ratio OR: In order to calculate a RR, we must have values for the incidence of the disease in

the exposed and the incidence in the non-exposed

• In CASE CONTROL STUDY: we CANNOT calculate incidence in exposed & non-exposed

• Therefore, in CASE CONTROL study, we CANNOT calculate RR directly

• We have to consider other type of measurement of association in a Case-control study

ODDS

• The ratio of the number of ways the event CAN OCCUR to the number of ways the

event CANNOT OCCUR

• Probability of event occur: P

• Probability of event CANNOT occur: 1 - P

• The odds of occurrence of the event:

§ Odds = P

1 - P

ODDS RATIO:

In BOTH

ad

bc represents the odds ratio (relative odds) in BOTH cohort and case-control studies

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