This document defines key terms used to estimate risk and potential for disease prevention. It discusses probability, risk, and odds, and how they differ. It then describes three main ways to estimate risk: absolute risk, relative risk, and odds ratio. Absolute risk is the probability of an outcome in a population without comparison. Relative risk compares risks between groups, such as exposed vs unexposed. Odds ratio specifically estimates the association between an exposure and outcome using case-control study designs. The document provides examples and interpretations for each term to demonstrate how to calculate and understand risk estimation.

1. Estimating Risk and Potential for Prevention
Dr. Faiza Abou El-Soud
Professor- Community Health Nursing
Menoufiya University - Egypt

2. ➢ Define difference between probability ,
risk, odds.
➢ Describe how to estimate risk (Absolute
Risk, Realtive Risk, Odds).
➢ Discuss how to calculate and interpret
the results of estimating risk

3. Definitions of terms
➢ • Probability: Is the (%) of times an event would occur if an
observation was repeated many times.
➢ • Risk: Is the probability of an event among those experiencing the event
divided by the who could experience it (at risk).
➢ • Odds: Probability of an divided by the probability of the event not
happening.

4. Difference between
Probability, Odds , Risk

5. Estimating Risk
The measures of association described in the following
section compare disease occurrence among one group (G1)
with disease occurrence in another group (G2).
These measures of association include:
(A)- Absolute Risk (AR)
(B)- Relative Risk (RR) = Risk Ratio
(C)-Attributable Risk

6. A- Absolute Risk
• The incidence of a disease in a population is termed
• Absolute risk is the chance that you will experience the outcome over some
period of time.
• can indicate the magnitude of risk in a group of people with
a certain ,
• but: It does not take into consideration the risk of disease in the
individuals,
It does not indicate whether the is associated with an increased
risk
of disease.
• Absolute risk doe not specify an .

7. Example
• What is the risk of having an ectopic pregnancy with various forms of
birth control?
• I have seen many women who have declined or at least been leery of an
intrauterine device (IUD) because of the increased risk of ectopic
pregnancy.
• The following shows the risk of having an ectopic pregnancy if you get
pregnant while using each of the following methods (these are crude
numbers; surprisingly there are no good data to inform these statistics and
estimates vary widely):
• No birth control – 2%
• Birth control pills/patch/ring – 3.5%
• Mirena IUD – 10%
• Paragard IUD – 5%
• Tubal occlusion/ligation – 25%

8. B-Relative Risk (A risk ratio -RR)
• Relative risk is the chance that you will experience the outcome
compared to someone else, based on individual risk factors or
circumstances.
• It compares the risk of a health event (disease, injury, risk factor,
or death) among one group with the risk among another group.
• It does so by dividing :
✓the risk (incidence proportion, attack rate) in group 1 by
✓the risk (incidence proportion, attack rate) in group 2.
• The two groups are typically differentiated by such demographic
factors as sex (e.g., males versus females) or by exposure to a
suspected risk factor (e.g., did or did not eat potato salad).

9. B-Relative Risk (A risk ratio -RR)
1- Attack Rate (Risk)
Attack rate for exposed = a ⁄ a+b
Attack rate for unexposed = c ⁄ c+d
Example:
• Risk of tuberculosis among East wing residents = 28 ⁄ 157 = 0.178 = 17.8%
• Risk of tuberculosis among West wing residents = 4 ⁄ 137 = 0.029 = 2.9%
• The risk ratio is simply the ratio of these two risks:
• Risk ratio = 17.8 ⁄ 2.9 = 6.1
• Thus, inmates who resided in the East wing of the dormitory were 6.1
times as likely to develop tuberculosis as those who resided in the West
wing.

10. B-Relative Risk
2.Relative risk (RR) - determination that a certain disease is associated with
a certain exposure.
Estimation of relative risks are vital in determining who will be at a
higher risk following the exposure.
 By using the ( ) and ( we can assess whether
there is an excess risk of disease in persons who have been exposed.
Comparing different risks among different groups the presence
of excessive risk (the incidence rate „attack rates‟ and the difference in
the risks).

11. Relative Risk (RR)
 and are designed to determine whether
there is an association between exposure to a factor and
development of a disease.
If an association exists, how strong is it?
 what is the ratio of the risk of disease in exposed
individuals to the risk of disease in nonexposed individuals?
(RR=relative risk).
Risk in exposed (incidence in the exposed)
Relative risk (RR) = Risk in non-exposed /
(incidence in the non-exposed)

12. Cohort Study Design

13. Example
•

14. Case Control Study Design

15. Example

16. Example

17. Interpretation of Relative Risk
( Measures the Strength of Association)

18. C. Odds ratio (OR)
• An odds ratio (OR) is between
an exposure and an outcome.
• The OR represents:
✓the odds that an will occur given a particular
, compared to
✓the odds of the occurring in the absence of
that exposure.
o Odds ratios are most commonly used in
✓Case-control studies,
✓Cross-sectional and Cohort study designs as well (with
some modifications and/or assumptions).

19. Odds ratio (OR)
•

20. Odds Ratio (OR)

21. Odds Ratio (OR)
In Case-Control and Cohort Studies

22. (c) - Attributable Risk
• How much of the disease that can be
to a certain exposure?
• Attributable risk is defined as the or
of disease incidence (or disease risk)
that can be attributed to a specific exposure.
Example
• How much of lung cancer risk experienced by
smokers can be attributed to smoking?

23. Attributable Risk
(ExposedandNon-ExposedGroup)

24. Example :

25. Interpretation

26. Attributable Risk
(TotalPopulation)

27. Example

28. Example

29. Thank You