Calculating relative/absolute risk (319/1700)

In a group of cancer pts, 10 died that wasn’t treated while 5 died in the tx group. Which
statement is correct?
a. Absolute risk =10
b. Relative risk =10
c. Relative risk =5
d. Absolute risk=5
e. Relative risk=2




























answer: D
because this is the incidence in the exposed

RR would be 5/10 =0.5

Absolute risk vs Relative risk explained

1. Relative risk : probability of an event happening

calculated by:

incidence in exposed group/incidence in non exposed

2. Relative risk reduction:

calculated by: (1 - Relative risk) x 100

3. Absolute risk: incidence in an exposed group

4. Absolute risk reduction(used if there was a favorable outcome):

control rate -  experimental rate

5. Absolute risk increase(used if there was an undesirable outcome):

experimental rate - control rate

6. Number needed to treat: calculated by

1 / ARR

For example:

1000 patients given a placebo, 20 died

1000 patients given a drug, 10 died

Relative risk= 10/20 = 0.5 ... meaning half as likely to die

Relative Risk Reduction = 1 - 0.5 x 100 = 50 % less likely to die

Absolute risk = 10/1000 for drug, 20/1000 for no treatment

Absolute risk reduction=0.02 - 0.01 = 0.01

Number needed to treat = 1/0.01 = 100