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Statistical Measures

Relative Risk & Odds Ratio

Relative Risk

Practice Exercise 8 Answer (round answers to one decimal place):

To calculate the relative risk, set up a two-by-two table:

Table 6
Number of Cases of Gastroenteritis by Exposure History,
Brown/Smith Wedding, Little Town, May 14, 2005
 
Gastroenteritis
  
 
Yes
No
Total
Ate potato salad
a
b
Didn't eat potato salad
c
d

  1. First calculate the risk of gastroenteritis among those that ate and those that didn't eat the potato salad:
    Risk among those that ate = a/(a + b) x 100 = / x 100 = %
    Risk among those that didn't eat = c/(c + d) x 100 = / x 100 = %

  2. Relative Risk (Risk Ratio)
    x = risk among those who ate the potato salad
    y = risk among those who didn't eat the potato salad
    Relative Risk = x/y x 1 = / x 1 =