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NNT Calculator

Enter the percentage of the control group and the experimental group in the calculator to estimate the Number Needed to Treat (NNT).

Your Outcomes:

Patient Years:

Experimental Group:

Related

The NNT calculator estimates the effectiveness of a medicine or treatment in a given population of patients.

What Is NNT?

The NNT (Number Needed to Treat) is the number of patients you need to treat to prevent one additional bad outcome (such as death or stroke). NNT statistics measure the effectiveness of a medicine or therapy in a population.

How to Calculate NNT?

The formula for NNT is:

NNT = 1 / ARR

Where ARR (Absolute Risk Reduction) is:

ARR = Control event rate - Experimental event rate

Example 1:

Find the NNT if the control group event rate is 15% and the experimental group is 10%.

Control group = 15% (0.15)
Experimental group = 10% (0.10)

Solution:

ARR = 0.15 - 0.10 = 0.05

NNT = 1 / 0.05 = 20

This means you need to treat 20 patients to prevent one adverse outcome.

Example 2:

Calculate the NNT if 300 patients are treated for 7 years, with a control group event rate of 20% and experimental group 10%.

Solution:

First, calculate the event rates per patient-year:

R₀ = 1 - e^(-Control Events / Time)

R₁ = 1 - e^(-Experimental Events / Time)

ARR = R₀ - R₁ = 0.1822

NNT = 1 / 0.1822 ≈ 5.49

This means you need to treat ~5.5 patients to prevent one adverse event.

Working of NNT Calculator

Input

Select percentage or patient-years from the dropdown
Enter patient-years, control group rate, and experimental group rate
Click Calculate

Output

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

FAQs

What is NNH?

NNH (Number Needed to Harm) is the number of patients that need to be treated for one patient to experience a harmful effect. An online NNH calculator can help estimate this using your dataset.

Is a low NNT better than a high NNT?

Yes. A lower NNT indicates a more effective treatment, while a higher NNT means the medicine is less effective.

References

From Wikipedia: Number Needed to Treat

From Psychiatrist.com: NNT, NNH, Number Needed to Harm Formula

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