Behavioral Science

Epidemiology and Research Design 205
MEASURES OF ASSOCIATION
Which measures are used to quantify
risks in population studies?
Which measure(s) of association is used
to evaluate cohort studies?
Which measure(s) of association is used
to evaluate case-control studies?
How does our four-box method
for calculating specificity and sensitivity
change when calculating risk?
Relative risk
Attributable risk
Odds ratio
Relative risk
Attributable risk
Odds ratio
The left heading of “test result” is
changed to “exposure/risk factor”
(the top heading stays the same).
+
Disease state
–
+
Exposure/risk
factor
–
a
c
b
d
RR = ([a/(a + b)] / [c/(c + d)])
AR = ([a/(a + b)] – [c/(c + d)])
OR = ad/bc
a = Exposed subjects with disease
b = Exposed subjects without disease
c = Unexposed subjects with disease
d = Unexposed subjects without disease
All with disease = (a + c)
All without disease = (b + d )
All exposed = (a + b)
All unexposed = (c + d )
Figure 26.2
What is relative risk (RR)?
How is RR calculated?
RR is a measure of the likelihood of
disease in exposed subjects compared
to unexposed. It is expressed as a ratio,
so an RR = 1.0 is the risk of the
unexposed subjects.
It is the incidence of disease in the
exposed group divided by the incidence
of disease in the unexposed group.
RR = [a/(a + b)]/[c/(c + d)]
At what value is RR significant? When RR is greater than or less than 1.0