Relative Risk Estimation With Examples and Their Interpretation

8/11/2019 Relative Risk Estimation With Examples and Their Interpretation

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Roll no. 73, 74, 79, 80.

RELATIVERISK


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Cohort Study

Cohort Study or Panel Study is a type ofanalytical (observational) study usually

undertaken to obtain additional evidenceto prove or disprove the existence of anassociation between suspected cause and

disease.


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Elements of a Cohort Study

1. Selection of study subjects.

2. Obtaining data on exposure.

3. Selection of comparisongroups.

4. Follow-up.5. Analysis.


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Analysis

Data analyzed in terms of:

Incidence Rates.

Estimation of risk.

Relative Risk

Attributable Risk.


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2 X 2 Table

DISEASERISKFACTOR

PRESENT ABSENT

PRESENT a b

ABSENT c d


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Relative Risk (RR)

Relative Risk is the ratio of theincidence of the disease among exposed

and the incidence among the non-exposed.

Aka riskratio.


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=

Note:

Numerator is not a part of the Denominator.

= +

=

+


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Interpretation

In a simple comparison between anexperimental group and a control group:

A relative risk of 1 means there is no

difference in risk between the two groups.RR of < 1 means the event is less likely tooccur in the experimental group than in thecontrol group.

RR of > 1 means the event is more likely tooccur in the experimental group than in thecontrol group.


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Examples

And their Interpretations


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Cigarette Smoking and Lung Cancer

DEVELOPEDLUNG

CANCERSMOKER

YES NO

YES 70 6930

NO 3 2997


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RR Estimation and Interpretation

Lung cancer incidence among smokers =70

70+6930=

70

7000= 10 per 1000

Lung cancer incidence among non-smokers=

3

3+2997=

3

3000= 1 per 1000

RR =

= 10

Smokers are 10 times at greater risk ofdeveloping lung cancer than non-smokers.


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Radiation Exposure and Cancer

CANCER

RADIATIONYES NO

YES 30 20

NO 10 90


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RR Estimation and Interpretation

Cancer incidence among those exposed to radiation =

30

30+20=

30

50= 60 per 100

Cancer incidence among those not exposed to radiation =

10

10+90=

10

100= 10 per 100

RR =

= 6

Those exposed to radiation are 6 times at greaterrisk of developing cancer than those not exposed.


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Conclusion

Thus, Relative Risk (RR) is a good measure todetermine if a factor leads to an increase, decrease orno effect on the development of some diseasesymptom.

RR=1No effect

RR1Leads to development of the disease


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Relative Risk Estimation With Examples and Their Interpretation

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