Lecture 18 9/24/24

Question 1

What is number needed to treat?

Answer 1

estimates the number of patients that need to be treated in order to have an impact on one individual

Question 2

How is number needed to treat calculated?

Answer 2

NNT = 1/ARR

Question 3

What is absolute risk reduction?

Answer 3

difference between the event rate in the control group and the event rate in the experimental group

Question 4

How is absolute risk reduction calculated?

Answer 4

-ARR = event rate in placebo group - event rate in treatment group
-ARR = old risk - new risk

Question 5

What are the interpretations for NNT value?

Answer 5

-perfect NNT is 1
-NNTs of 2-5 represent effective therapies
-NNTs of 20 or above may be useful in prophylaxis

Question 6

What is relative risk reduction?

Answer 6

new risk/old risk

Question 7

What is number needed to harm?

Answer 7

estimate of the number of patients that need to be treated in order to have a specific side effect in one individual

Question 8

How is NNH calculated?

Answer 8

NNH = 1/absolute harm increase

Question 9

How is absolute harm increase calculated?

Answer 9

absolute harm increase = event rate in treated group - event rate in placebo group

Question 10

Which assessment of risk reduction is better?

Answer 10

absolute risk reduction is better than relative risk reduction

Question 11

What are the take home points regarding NNT?

Answer 11

-certain individuals will never experience a bad outcome regardless of risk
-some individuals will not have a positive outcome even with treatment
-some individuals will benefit from an effective drug
-NNT is a comparative measure of effect
-very high NNT is least desirable
-different risk groups/outcomes can result in different NNTs
-NNT varies over time

Question 12

How should NNT compare to NNH?

Answer 12

want NNT to be a lower number than NNH for any side effect