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##### Asked by: Tawfik Iturriazpe

medical health cancer# What is a high number needed to treat?

Last Updated: 1st March, 2020

**treatment**and no one improves with control. A

**higher**NNT indicates that

**treatment**is less effective. NNT is similar to

**number needed to harm**(NNH), where NNT usually refers to a therapeutic intervention and NNH to a detrimental effect or risk factor.

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Herein, what does number needed to harm mean?

The **number needed to harm** (NNH) is an epidemiological measure that indicates how many persons on average need to be exposed to a risk factor over a specific period to cause **harm** in an average of one person who **would** not otherwise have been **harmed**.

One may also ask, how is NNT calculated in study? **Calculation**

- The NNT is the inverse of the absolute risk reduction (ARR).
- The ARR is the absolute difference in the rates of events between a given activity or treatment relative to a control activity or treatment, ie control event rate (CER) minus the experimental event rate (EER), or ARR = CER - EER.

In this manner, how do you calculate number needed to harm?

From this the value known as the **number needed to harm** (**NNH**) can be **calculated** by dividing 1 by the absolute risk increase, and again multiplying by 100 when the ARI is expressed as a percentage. **NNH** shows how many individuals would need to be treated with the drug in order for 1 to show the harmful effect.

When can you calculate NNT?

The **NNT** is simply the inverse of the ARR; it **can** be **calculated** by taking 100 and dividing it by the ARR (1).