Risk Concepts_9_9_24_Dadason.ppt for clinician

Risk concept

1. Risk Concepts
By: Dada Robert
BPH, Dip CM&PH

2. Concept of Measuring Risk

To every disease event or outcome, there is a risk or
risks.

The risk of a disease event is measured in three ways:
i. Relative risk,
ii. Attributable risk,
iii. Absolute risk.

3. Relative risk (RR)

It is ratio of incidence of the disease among the exposed and
incidence among the non-exposed.
RR (incidence of disease among exposed)/
(Incidence of disease among non-exposed)
=a/(ab)/c/(cd)
=28/17.4
=1.6

If RR is more than 1, then there is a positive association

If RR is equal to 1, then there is no association

Smokers develop CHD 1.6 times more than nonsmokers.

4. Relative risk (RR)

Expresses risk of developing a diseases in exposed
group (a + b) as compared to non-exposed group (c
+ d)
RR= Incidence (risk) among exposed
Incidence (risk) among non-exposed
RR= a/(a+b)
c/(c+d)

5. Interpretation of relative risk
What does a RR of 2 mean?
Risk in exposed =RRX Risk in non-exposed
RR of 2 means
Risk in exposed=2X Risk in non-exposed
Thus a relative risk of 2 means the exposed
group is two times at a higher risk when
compared to non-exposed

6. Attributable Risk (AR)

AR indicates how much of the risk is due to
/attributable/ to the exposure
Quantifies the excess risk in the exposed that can
be attributable to the exposure by removing the
risk of the disease occurred due to other causes
AR= Risk (incidence) in exposed- Risk (incidence)
in non-exposed
AR= {a/(a+b)} / {c/(c+d)))}
Attributable risk is also called risk difference

7. Attributable risk (AR)

This is defined as amount or proportion of disease
incidence that can be attributed to a specific exposure.

It indicates to what extent the disease under study can be
attributed to the exposure:
(incidence of disease among exposed)
- (incidence of disease among non exposed)/
(Incidence of disease among exposed)

8. Example

The incidence of colon cancer disease
among cigarette smokers is 28.

The incidence of the same disease
among the non-smokers is 17.4

Calculate the attributable risk of the
disease to the population at risk.

9. Solution

AR= Risk (incidence) in exposed- Risk
(incidence) in non-exposed
AR=28-17.4/28
=10.6/28
= 0.379
= 37.9%

37. 9% of colon cancer disease among
the smokers was due to smoking.

10. Interpreting AR

What does attributable risk of 10 mean?

10 of the exposed cases are attributable to
the exposure.

By removing the exposure one can prevent
10 cases from getting the disease.

11. Attributable risk percent (AR%)

Estimates the proportion of disease among the
exposed that is attributable to the exposure.


The proportion of the disease in the exposed that
can be eliminated by eliminating the exposure

AR%=(Risk in exposed – Risk in non expose) X100%
Risk in exposed

12. Interpretation of AR%

What does AR% of 10% mean?

10% of the disease can be attributed to the
exposure.

10% of the disease can be eliminated if we
avoid the exposure.

13. Population Attributable Risk (PAR)

Estimates the rate of disease in the total
population that is attributable to exposure.

PAR = Risk in population – Risk in unexposed.

PAR = Prevalence rate of exposure.

14. Population attributable risk percent
(PAR%)


Estimates the proportion of disease in the
study population that is attributable to
exposure and thus could be eliminated if the
exposure were eliminated.

PAR%= Risk in population – Risk in unexposed
Risk in population

15. Possible outcomes in studying the
relationship between exposure &
disease
1.No association
RR=1
AR=0
2. Positive association
RR>1
AR>0
3. Negative association
RR<1 (fraction)
AR<0 (Negative)

16. Absolute Risk

Also called incidence

Incidence enables us to determine a person's
probability of being diagnosed with a disease during
a given time.

Hence, incidence is the number of new cases
diagnosed with a disease.

Because it deals with new disease events,
incidence is a measure of risk.

An incidence rate is the number of new cases of a
disease divided by the number of persons at risk for
the disease per a constant population.

17. Odds ratio

It is a measure of strength of association between the
risk factor and outcome.

The derivation of the odds ratio is based on three
assumptions:

●
The disease being investigated is relatively rare

●
The cases must be representative of those with the
disease

●
The controls must be representative of those without the
disease.

18. Odds ratio a.d/b.c
33X27/55X2 = 8.1

People who smoke less than 5 cigarettes per
day showed a risk of having lung cancer 8.1
times higher as compared to non-smokers.

19. 
OR is > 1- "those with the disease are more
likely to have been exposed,"
OR close to 1 then the exposure and disease
are not likely associated.
OR <1-exposure is a protective factor in the
causation of the disease.

20. Thanks for listening
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