Number Needed to Harm (NNH) Calculator
Calculate the Number Needed to Harm (NNH) with our interactive, accessible tool. Designed for healthcare professionals to assess treatment side effects.
Interactive Calculator
Full original guide (expanded)
Number Needed to Harm (NNH) Calculator
This calculator helps healthcare professionals determine the Number Needed to Harm (NNH), which indicates how many patients need to be exposed to a risk factor for one patient to experience harm. It assists in evaluating the side effects of medical treatments.
Data Source and Methodology
All calculations are rigorously based on statistical formulas for epidemiological studies. For further reading, refer to clinical guidelines and scientific literature.
The Formula Explained
NNH = 1 / (Incidence in Treated Group - Incidence in Control Group)
Glossary of Terms
- Incidence in Treated Group (%): The percentage of patients experiencing the event in the treatment group.
- Incidence in Control Group (%): The percentage of patients experiencing the event in the control group.
- NNH: A measure indicating how many patients need to be treated for one to be harmed.
How It Works: A Step-by-Step Example
Consider a drug trial where 5% of the treated group and 2% of the control group experience a certain side effect. The NNH would be calculated as follows:
NNH = 1 / (0.05 - 0.02) = 33.33
Frequently Asked Questions (FAQ)
What is NNH?
Number Needed to Harm (NNH) is a measure used in epidemiology to describe the effectiveness of a treatment in terms of adverse effects.
How is NNH calculated?
NNH is calculated using the formula: NNH = 1 / (Incidence in Treated Group - Incidence in Control Group).
Why is NNH important?
NNH helps in understanding the risk of adverse effects from a treatment, aiding in informed decision-making.
Can NNH be a negative number?
No, NNH should always be a positive number. If the calculation results in a negative number, it indicates that the treatment is beneficial rather than harmful.
What is the difference between NNH and NNT?
While NNH measures harm, Number Needed to Treat (NNT) measures the effectiveness of a treatment in achieving a beneficial outcome.
Formula (LaTeX) + variables + units
','
NNH = 1 / (Incidence in Treated Group - Incidence in Control Group)
NNH = 1 / (0.05 - 0.02) = 33.33
- No variables provided in audit spec.
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.
Number Needed to Harm (NNH) Calculator
This calculator helps healthcare professionals determine the Number Needed to Harm (NNH), which indicates how many patients need to be exposed to a risk factor for one patient to experience harm. It assists in evaluating the side effects of medical treatments.
Interactive Calculator
Data Source and Methodology
All calculations are rigorously based on statistical formulas for epidemiological studies. For further reading, refer to clinical guidelines and scientific literature.
The Formula Explained
NNH = 1 / (Incidence in Treated Group - Incidence in Control Group)
Glossary of Terms
- Incidence in Treated Group (%): The percentage of patients experiencing the event in the treatment group.
- Incidence in Control Group (%): The percentage of patients experiencing the event in the control group.
- NNH: A measure indicating how many patients need to be treated for one to be harmed.
How It Works: A Step-by-Step Example
Consider a drug trial where 5% of the treated group and 2% of the control group experience a certain side effect. The NNH would be calculated as follows:
NNH = 1 / (0.05 - 0.02) = 33.33
Frequently Asked Questions (FAQ)
What is NNH?
Number Needed to Harm (NNH) is a measure used in epidemiology to describe the effectiveness of a treatment in terms of adverse effects.
How is NNH calculated?
NNH is calculated using the formula: NNH = 1 / (Incidence in Treated Group - Incidence in Control Group).
Why is NNH important?
NNH helps in understanding the risk of adverse effects from a treatment, aiding in informed decision-making.
Can NNH be a negative number?
No, NNH should always be a positive number. If the calculation results in a negative number, it indicates that the treatment is beneficial rather than harmful.
What is the difference between NNH and NNT?
While NNH measures harm, Number Needed to Treat (NNT) measures the effectiveness of a treatment in achieving a beneficial outcome.
Formula (LaTeX) + variables + units
','
NNH = 1 / (Incidence in Treated Group - Incidence in Control Group)
NNH = 1 / (0.05 - 0.02) = 33.33
- No variables provided in audit spec.
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.
Number Needed to Harm (NNH) Calculator
This calculator helps healthcare professionals determine the Number Needed to Harm (NNH), which indicates how many patients need to be exposed to a risk factor for one patient to experience harm. It assists in evaluating the side effects of medical treatments.
Interactive Calculator
Data Source and Methodology
All calculations are rigorously based on statistical formulas for epidemiological studies. For further reading, refer to clinical guidelines and scientific literature.
The Formula Explained
NNH = 1 / (Incidence in Treated Group - Incidence in Control Group)
Glossary of Terms
- Incidence in Treated Group (%): The percentage of patients experiencing the event in the treatment group.
- Incidence in Control Group (%): The percentage of patients experiencing the event in the control group.
- NNH: A measure indicating how many patients need to be treated for one to be harmed.
How It Works: A Step-by-Step Example
Consider a drug trial where 5% of the treated group and 2% of the control group experience a certain side effect. The NNH would be calculated as follows:
NNH = 1 / (0.05 - 0.02) = 33.33
Frequently Asked Questions (FAQ)
What is NNH?
Number Needed to Harm (NNH) is a measure used in epidemiology to describe the effectiveness of a treatment in terms of adverse effects.
How is NNH calculated?
NNH is calculated using the formula: NNH = 1 / (Incidence in Treated Group - Incidence in Control Group).
Why is NNH important?
NNH helps in understanding the risk of adverse effects from a treatment, aiding in informed decision-making.
Can NNH be a negative number?
No, NNH should always be a positive number. If the calculation results in a negative number, it indicates that the treatment is beneficial rather than harmful.
What is the difference between NNH and NNT?
While NNH measures harm, Number Needed to Treat (NNT) measures the effectiveness of a treatment in achieving a beneficial outcome.
Formula (LaTeX) + variables + units
','
NNH = 1 / (Incidence in Treated Group - Incidence in Control Group)
NNH = 1 / (0.05 - 0.02) = 33.33
- No variables provided in audit spec.
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Last code update: 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.