POPM 3240 Exam | Questions & Answers (100 %Score) Latest Updated 2024/2025
Comprehensive Questions A+ Graded Answers | With Expert Solutions
What measures are used to determine the strength of the relationship between an exposure and an
outcome? Effect of an exposure in causing an outcome? - Measures of association --> relative risk (RR),
odds ratio (OR), incidence rate ratio (IRR)
Measures of effect -->
i) in an exposed group: risk difference (RD), attributable proportion exposed
ii) in a population: population attributable risk (PAR), population attributable fraction (PAF)
What is relative risk? How is it calculated and interpreted? - Relative risk is a ratio of 2 probabilities and
is calculated as follows:
RR = P(D+|E+)/P(D+/E-)
An RR> 1 means that the exposed group is more likely to show the outcome than the non-exposed
group while an RR<1 means the exposed group is less likely than the non-exposed group to show the
outcome.
What are odds ratios? How are they calculated and interpreted? - Odds ratios are ratios of 2 odds and
are calculated as follows:
OR = (odds of disease/exposure in the exposed/diseased group)/(odds of disease/exposure in the non-
exposed/non-diseased group)
or : OR = (ad)/(bc)
In cohort studies --> an OR >1 means that the odds of disease are greater in the exposed group than the
non-exposed group
, In case-control studies --> an OR >1 means that the odds of exposure are greater in the diseased group
than the non-diseased group
Under what circumstances do the RR and OR closely approximate each other? - The RR and OR closely
approximate each other when the outcome of interest is a rare disease.
What are incidence rate ratios? How are they calculated and interpreted? - The incidence rate ratio is a
ratio of incidence rates between 2 groups and is calculated as follows:
IRR = incidence rate of disease in exposed group/incidence rate of disease in a non-exposed group
or: IRR = (a1/t1)/(ao/to)
An IRR >1 means that incidence rate of disease in the exposed group is greater than the incidence rate in
the non-exposed group
What is risk/rate difference? How is it calculated and interpreted? - Risk/rate differences measure the
difference in risk or rate of the outcome in the exposed and non-exposed groups.
Risk difference = P(D+|E+) - P(D+|E-)
Rate difference = (rate in E+) - (rate in E-)
The RD>0 represents the excess risk/rate of the outcome in the exposed group.
What is the attributable proportion exposed? How is it calculated and interpreted? - The AP measures
the proportion of risk or rate of the outcome in the exposed group that is attributable to the exposure.
For risk data: AP = risk difference/P(D+/E+)
For rate data: AP = rate difference/(rate in E+)
The AP represents the % of the outcome in the exposed group that is caused by exposure.
Comprehensive Questions A+ Graded Answers | With Expert Solutions
What measures are used to determine the strength of the relationship between an exposure and an
outcome? Effect of an exposure in causing an outcome? - Measures of association --> relative risk (RR),
odds ratio (OR), incidence rate ratio (IRR)
Measures of effect -->
i) in an exposed group: risk difference (RD), attributable proportion exposed
ii) in a population: population attributable risk (PAR), population attributable fraction (PAF)
What is relative risk? How is it calculated and interpreted? - Relative risk is a ratio of 2 probabilities and
is calculated as follows:
RR = P(D+|E+)/P(D+/E-)
An RR> 1 means that the exposed group is more likely to show the outcome than the non-exposed
group while an RR<1 means the exposed group is less likely than the non-exposed group to show the
outcome.
What are odds ratios? How are they calculated and interpreted? - Odds ratios are ratios of 2 odds and
are calculated as follows:
OR = (odds of disease/exposure in the exposed/diseased group)/(odds of disease/exposure in the non-
exposed/non-diseased group)
or : OR = (ad)/(bc)
In cohort studies --> an OR >1 means that the odds of disease are greater in the exposed group than the
non-exposed group
, In case-control studies --> an OR >1 means that the odds of exposure are greater in the diseased group
than the non-diseased group
Under what circumstances do the RR and OR closely approximate each other? - The RR and OR closely
approximate each other when the outcome of interest is a rare disease.
What are incidence rate ratios? How are they calculated and interpreted? - The incidence rate ratio is a
ratio of incidence rates between 2 groups and is calculated as follows:
IRR = incidence rate of disease in exposed group/incidence rate of disease in a non-exposed group
or: IRR = (a1/t1)/(ao/to)
An IRR >1 means that incidence rate of disease in the exposed group is greater than the incidence rate in
the non-exposed group
What is risk/rate difference? How is it calculated and interpreted? - Risk/rate differences measure the
difference in risk or rate of the outcome in the exposed and non-exposed groups.
Risk difference = P(D+|E+) - P(D+|E-)
Rate difference = (rate in E+) - (rate in E-)
The RD>0 represents the excess risk/rate of the outcome in the exposed group.
What is the attributable proportion exposed? How is it calculated and interpreted? - The AP measures
the proportion of risk or rate of the outcome in the exposed group that is attributable to the exposure.
For risk data: AP = risk difference/P(D+/E+)
For rate data: AP = rate difference/(rate in E+)
The AP represents the % of the outcome in the exposed group that is caused by exposure.
