Preventable fraction among the unexposed

In epidemiology, preventable fraction among the unexposed (PFu), is the proportion of incidents in the unexposed group that could be prevented by exposure. It is calculated as [math]\displaystyle{ PF_u = (I_u - I_e)/I_u = 1 - RR }[/math], where [math]\displaystyle{ I_e }[/math] is the incidence in the exposed group, [math]\displaystyle{ I_u }[/math] is the incidence in the unexposed group, and [math]\displaystyle{ RR }[/math] is the relative risk.[1][2] It is a synonym of the relative risk reduction. It is used when an exposure reduces the risk, as opposed to increasing it, in which case its symmetrical notion is attributable fraction among the exposed.[citation needed]

## Contents

* 1 Numerical example
* 2 See also
* 3 References

## Numerical example

| Example of risk reduction

|

Experimental group (E)  | Control group (C)  | Total
Events (E)  | EE = 15  | CE = 100  | 115
Non-events (N)  | EN = 135  | CN = 150  | 285
Total subjects (S)  | ES = EE + EN = 150  | CS = CE + CN = 250  | 400
Event rate (ER)  | EER = EE / ES = 0.1, or 10%  | CER = CE / CS = 0.4, or 40%  |
Equation | Variable | Abbr. | Value

|
|
|

CER - EER | absolute risk reduction  | ARR | 0.3, or 30%
(CER - EER) / CER  | relative risk reduction | RRR  | 0.75, or 75%
1 / (CER − EER) | number needed to treat | NNT | 3.33
EER / CER | risk ratio | RR | 0.25
(EE / EN) / (CE / CN) | odds ratio | OR | 0.167
(CER - EER) / CER | preventable fraction among the unexposed | PFu | 0.75

## See also

* Population Impact Measures
* Preventable fraction for the population

## References

1. ↑ Aschengrau, Ann; Seage, George R. (2014). Essentials of epidemiology in public health (3rd ed.). Burlington, MA: Jones & Bartlett Learning. pp. 67. ISBN 9781449657338. OCLC 826123155.
2. ↑ Rothman, Kenneth J.; Greenland, Sander; Lash, Timothy L. (2012). Modern epidemiology (3rd ed.). Philadelphia: Lippincott Williams & Wilkins. ISBN 9780781755641. OCLC 169455558.

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Clinical research and experimental design

Overview|

* Clinical trial
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Controlled study
(EBM I to II-1)|

* Randomized controlled trial
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Observational study
(EBM II-2 to II-3)|

* Cross-sectional study vs. Longitudinal study, Ecological study
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Measures|

| Occurrence|

Incidence, Cumulative incidence, Prevalence, Point prevalence, Period prevalence

|

Association|

Risk difference, Number needed to treat, Number needed to harm, Risk ratio, Relative risk reduction, Odds ratio, Hazard ratio

Population impact|

Attributable fraction among the exposed, Attributable fraction for the population, Preventable fraction among the unexposed, Preventable fraction for the population

Other|

Clinical endpoint, Virulence, Infectivity, Mortality rate, Morbidity, Case fatality rate, Specificity and sensitivity, Likelihood-ratios, Pre- and post-test probability

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Interpretation of results|

* Selection bias
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* Null result

* Category
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