Can you calculate the number needed to treat with the provided data? Hint: calculate the absolute risk reduction first.

A nephrology (kidney) clinic performs a randomized clinical trial using an investigational blood pressure lowering method that is injection based. The patients are assigned randomly to either the intervention or to sham or placebo method. There are 100 participants in each arm of the trial.

47 of the intervention see a meaningful improvement in blood pressure. 21 of the placebo method see a meaningful improvement in blood pressure

Number needed to treat

Can you calculate it?

Please answer the following questions:

What is the number needed to treat in this trial?

The number needed to treat (NNT) is defined as 1/ARR or the absolute risk reduction.
The ARR is the absolute difference between the intervention group and the control, using the percent improvement.

The absolute benefit is 47/100 – 21/100 or 26%.

The number needed to treat is 1/0.26 or 3.8.

Number needed to treat is interpreted as a whole number (1 patient).

So for this trial, for every 4 patients given this new method to treat blood pressure, one patient will have meaningful blood pressure reduction.

What does Absolute Risk Reduction (ARR) measure?
A
The percentage of patients who experience side effects
B
The difference in event rates between experimental and control groups
C
The total number of patients treated
D
The average age of participants in a study

B
The difference in event rates between experimental and control groups

Why is ARR considered a meaningful metric?
A
It maintains the baseline rate of the outcome
B
It provides a relative comparison of risks
C
It is easier to calculate than NNT
D
It is always a positive value

A
It maintains the baseline rate of the outcome

How is the Number Needed to Treat (NNT) calculated?
A
NNT = 1 / ARR
B
NNT = ARR x 100
C
NNT = ARR / 2
D
NNT = ARR + 1

A
NNT = 1 / ARR

What is a key characteristic of NNT?
A
It must be rounded up to the nearest whole number
B
It is always less than 1
C
It can be a decimal value
D
It is calculated using relative risk

A
It must be rounded up to the nearest whole number

Absolute Risk Reduction (ARR) and Number Needed to Treat (NNT)

Definition of Absolute Risk Reduction (ARR)

The Absolute Risk Reduction (ARR), also referred to as the absolute risk difference, is a statistical measure used to evaluate the efficacy of an intervention. It quantifies the difference between the event rates in the experimental group and the control group.

Importance of ARR

ARR is considered a meaningful metric for assessing and reporting risk reduction for several reasons:
* It maintains the baseline rate of the outcome, providing a clearer picture of the actual risk.
* It avoids exaggerating the benefits of an intervention by presenting data in absolute terms rather than relative terms.

Calculating Number Needed to Treat (NNT)

ARR can calculate the Number Needed to Treat (NNT), which is a valuable measure for estimating the effect size of an intervention. NNT indicates how many patients need to be treated to prevent one additional adverse outcome.

Formula for NNT

The NNT is calculated as the reciprocal of the ARR expressed as a decimal:

* NNT = 1 / ARR

It is important to note that NNT is rounded up to the nearest whole number, as it must be interpreted as a count of patients.

Example of NNT Calculation

In the example above, the NNT was determined to be 4. This means that for every 4 patients treated with a new anti-hypertensive method, one additional patient will experience a beneficial effect in terms of blood pressure reduction.

Inspiration: Number needed to treat (NNT) in clinical literature: an appraisal, National Library of Medicine

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