Scribd
Upload
84 views24 pages

Estimation of Risks

This document discusses key concepts for estimating risks in epidemiological studies, including relative risk, odds ratio, attributable risk, and population attributable risk. It provides examples of calculating each measure using data from epidemiological studies. Relative risk compares the risk of disease between exposed and unexposed groups. Odds ratio makes the same comparison but is used in case-control studies when the disease is rare. Attributable risk is the difference in disease rates between exposed and unexposed, and population attributable risk estimates how much disease could be reduced by eliminating an exposure.

Uploaded by

Dr mayuri rotti
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPTX, PDF, TXT or read online on Scribd
84 views24 pages

Estimation of Risks

This document discusses key concepts for estimating risks in epidemiological studies, including relative risk, odds ratio, attributable risk, and population attributable risk. It provides examples of calculating each measure using data from epidemiological studies. Relative risk compares the risk of disease between exposed and unexposed groups. Odds ratio makes the same comparison but is used in case-control studies when the disease is rare. Attributable risk is the difference in disease rates between exposed and unexposed, and population attributable risk estimates how much disease could be reduced by eliminating an exposure.

Uploaded by

Dr mayuri rotti
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPTX, PDF, TXT or read online on Scribd
You are on page 1/ 24

Estimation of risks in

epidemiological studies.
In this class you will learn to calculate
• Relative risk
• Odds ratio
• Attributable risk
• Population attributable risk
RELATI
VE RISK
Relative risk (risk ratio)
• It is the ratio of the incidence of the disease (or death) among
exposed and the incidence among non-exposed.

RR=
It is a direct measure of strength of association between suspected
cause and effect.
A relative risk of one indicates no association.
RR of more than one indicates positive association between exposure
and disease under study.
It is useful to consider 95% confidence interval of a RR since it
provides an indication of likely and maximum levels of risk.
Usually calculated in cohort studies.
Example 1.
• In a rural area,100 women were selected who conceived during the
pesticide spraying season and another group of 100 women were
selected living in the same area who conceived during non-spraying
season.
The number of miscarriages in both the groups was recorded. The
number of miscarriages was 30 in those exposed to pesticides and 10 in
those not exposed.
Exposed to pesticides Miscarriage Total

Yes No

yes 30 (a) 70 (b) 100

no 10 (c) 90 (d) 100

Total 40 160 200


• RR=

RR=

=0.3/0.1=3
Example 2.
• To study the strength of association between heavy work during ante-
natal period and low birth weight baby, cohort of 515 heavy worker
ANCs was followed up. A duly matched control cohort of 515
sedentary-moderate worker ANCs were also followed up. Complete
follow up till the measurement of birth weight could be done in 506
and 511 subjects of study and control cohort respectively. Following
outcomes were found
Type of ANC Low birth weight

Present Absent

Heavy worker 189 317 506

Sedentary-moderate 95 416 511

284 733 1017


RR=

=2.05
 Heavy worker pregnant ladies are at 2 times higher risk of having low
birth weight babies than sedentary-moderate worker.
ODDS
RATIO
Odds ratio
It is the ratio of the odds (chance) of an event occurring in one group to
the odds of it occurring in another group.

OR= ad/bc
• Calculated in case-control studies

• If the disease under study is very rare then odds ratio can be used as
relative risk.
Example 1.
• A study was launched to determine if smoking increased the risk of
stroke. Fifty patients diagnosed with stroke and 50 matching healthy
persons were assessed for their smoking status. Thirty of the stroke
patients were smokers as against 20 among healthy. Calculate the
effect of smoking on the risk of stroke.
H/O Smoking Stroke
Yes No
Present 30 20 50

Absent 20 30 50

Total 50 50 100
• OR =

=2.2
 smokers are at 2.2 times risk of stroke than non-smokers.
Example 2.
• One study was conducted to demonstrate the effect of physical
exercise on heart diseases. Around 100 patients with coronary heart
disease were enrolled and 100 matching controls were selected. It
was found that 60 of controls were doing daily physical exercise
whereas only 10 of cases were doing regular exercises. Calculate the
odds ratio.
H/O exercise Coronary artery disease
Present Absent
Present 10 60 70

Absent 90 40 130

100 100 200


ATTRIBUTA
BLE RISK
Attributable risk
• It is the difference in incidence rates of disease (or death) between an
exposed group and non-exposed group.

• AR= ×100
• Attributable risk indicates to what extent the disease under study can
be attributed to the exposure.
POPULATIO
N
ATTRIBUTA
BLE RISK
Population attributable risk (PAR)
It is the incidence of the disease (or death) in the total population
minus the incidence of the disease (or death) among those who were
not exposed to the suspected causal factor.

 The PAR provides an estimate of amount by which the disease could


be reduced in that population if the suspected risk factor was
eliminated or modified.

You might also like