Absolute and relative risk

Question 1

What is an absolute risk?

Answer 1

• a probabilty (event rate)

Question 2

What is the control event rate?

Answer 2

e.g.
80/100 patients remain ill without treatment, then the control risk of remaining ill is 0.8/80%

Question 3

What is experimental event rate?

Answer 3

20/100 patients get ill with treatment , then the risk of getting ill with treatment is 0.2/20%

Question 4

What is absolute this reduction?

Answer 4

The difference between the treatment risk and the control risk or the experimental and control event rate.

Control event rate- Experimental event rate

Question 5

What is relative risk?

Answer 5

• The treatment risk of getting ill as a proportion of the control risk of remaining ill
• Experimental event rate/ control event rate = treatment risk of remaining ill/ control risk of remaining ill

Question 6

What is relative risk reduction?

Answer 6

• the absolute risk reduction as a fraction of the control absolute risk
• control event rate- treatment event rate/ control event rate

1- treatment event rate/ control event rate
1- relevant risk

Question 7

What is the number needed to treat?

Answer 7

• the number of people you’d need to treat to acheive the event of interest once