Resources
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Glossary
- Absolute risk reduction (ARR): difference between the control event rate and the experimental event rate, expressed as a percentage
ARR = CER – EER - Confidence Interval (Cl): tells you the range of values within which the true value could feasibly lie, given the size of the difference observed.
- Control event rate (CER): proportion of patients who experience an outcome in the control group
- Experimental event rate (EER): proportion of patients who experience an outcome in the experimental group
- Number needed to treat (NNT): the number of patients that would need to be treated in order for ONE on them to have the beneficial outcome.
It is calculated by calculating the reciprocal (or inverse) of the ARR.
NNT = 1 / ARR
Note: if the ARR is expressed as a percentage (%) then:
NNT = 1/ARR x 100
or 100/ARR - Number needed to harm (NNH): the number of patients that would need to be treated in order for ONE on them to experience the adverse outcome.
It is calculated by calculating the reciprocal (or inverse) of the absolute risk increase (ARI)
NNH = 1/ARI
Note: if the ARI is expressed as a percentage (%) then:
NNH = 1/ARI x 100
or 100/ARI - Relative risk reduction (RRR): difference in event rates relative to (or proportional to) the control event rate, expressed as a percentage
RRR = (CER – EER) / CER - Surrogate Outcome: should reflect the treatment effect on an important clinical endpoint, but does not directly measure the clinical endpoint itself.
Resources
| Title/link | Description |
|---|---|
| Using evidence to guide practice: what information is useful? | How to source the most useful evidence on the efficacy of interventions |
| RLO: Confidence Intervals | Defines the term 'confidence intervals' and demonstrates how they can be used to determine the significance and range of possible sizes of a treatment effect. |
| RLO: Numbers needed to treat (NNT) and numbers needed to harm (NNH) | Defines the term 'confidence intervals' and demonstrates how they can be used to determine the significance and range of possible sizes of a treatment effect. |
| RLO: Positive and Negative Predictive Value of Diagnostic Tests | Defines the term 'confidence intervals' and demonstrates how they can be used to determine the significance and range of possible sizes of a treatment effect. |
| RLO: Relative Risk Reduction (RRR) and Absolute Risk Reduction (ARR) | This RLO considers how to measure and interpret the magnitude of effect in clinical trial results using relative risk reduction (RRR) and absolute risk reduction (ARR). |
| RLO: Surrogate Outcomes | Considers the type of evidence which should be used when making decisions about patient care. |
Books and Journals
| Bee, H and Boyd, D. (2004) The Developing Child 10th ed.. Pearson. |
| Blakemore, SJ and Frith, U. (2005) The Learning Brain: lessons for education. Oxford: Blackwell. |
Determining the Clinical Importance of Trial Results - Print summary
This RLO covers how to determine the clinical importance of trial results.
Learning outcomes
By completing this resource, you will have learnt how to:
- interpret information on the relevance, size and precision of the effect of an intervention
- calculate ARR and NNT
By completing this resource, you will have learnt how to:
- interpret information on the relevance, size and precision of the effect of an intervention
- calculate ARR and NNT
This resource was developed by:
Elaine Bentley, Julia Lacey, Briony Leighton - content authors
Neil Duffin, Liz Hilton - developers
The resource was originally funded by RLO-CETL.
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