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What is risk?
What is risk?
An estimation of the likelihood of an outcome in a specified population, over a specified time period.
Which of the following measures can be used to quantify excess risk? (Select all that apply)
Which of the following measures can be used to quantify excess risk? (Select all that apply)
Risk = Cumulative incidence in the population (Ic) = # of events in a specified time frame / _____
Risk = Cumulative incidence in the population (Ic) = # of events in a specified time frame / _____
in population at risk
What does RD = 0 indicate?
What does RD = 0 indicate?
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What can be used to calculate excess risk besides incidence measures?
What can be used to calculate excess risk besides incidence measures?
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Risk Ratio is equal to the incidence in exposed divided by the incidence in unexposed.
Risk Ratio is equal to the incidence in exposed divided by the incidence in unexposed.
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Which of the following formulas represents Attributable Risk (AR)?
Which of the following formulas represents Attributable Risk (AR)?
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What is the relationship between Risk Difference and Attributable Risk?
What is the relationship between Risk Difference and Attributable Risk?
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What does the Population Attributable Risk Percent (PAR%) indicate?
What does the Population Attributable Risk Percent (PAR%) indicate?
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When is the Odds Ratio a good estimate of the Risk Ratio?
When is the Odds Ratio a good estimate of the Risk Ratio?
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Vaccine Efficacy = Iunvacc. – Ivacc. x _____
Vaccine Efficacy = Iunvacc. – Ivacc. x _____
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Attributable Risk Percentage can only be used for established causal associations.
Attributable Risk Percentage can only be used for established causal associations.
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What does the term 'exposed' refer to in terms of cases above?
What does the term 'exposed' refer to in terms of cases above?
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Study Notes
Measures of Excess Risk
- Risk is an estimation of the likelihood of an outcome in a specified population over a specified time period.
- It can be calculated as the cumulative incidence in the population (Ic) or the incidence rate.
- Epidemiologists often use "risk" to refer to both cumulative incidence and incidence rate measures.
Cumulative Incidence (Ic)
- Calculated as the number of events (e.g., lung cancer cases) in a specified time frame divided by the number of people at risk in the population.
- Assumes the population at risk remains constant.
Incidence Rate
- Calculated as the number of events (e.g., lung cancer cases) divided by the total person-time of follow-up.
- Can be used to calculate excess risk measures.
Excess Risk Measures
- Used to quantify the association between an exposure and an outcome.
- Excess risk measures include:
- Risk Difference (RD)
- Risk Ratio (RR)
- Attributable Risk (AR)
- Attributable Risk Percent (AR%)
- Population Attributable Risk (PAR)
- Population Attributable Risk Percent (PAR%)
Risk Difference (RD)
- Calculated as the incidence in the exposed group minus the incidence in the unexposed group (Ie - Io).
- Interpreted as the excess risk of the outcome due to exposure.
Risk Ratio (RR)
- Calculated as the incidence rate in the exposed group divided by the incidence rate in the unexposed group (Ie / Io).
- Interpreted as the strength of the association between exposure and outcome.
Attributable Risk (AR)
- Calculated as the incidence in the exposed group minus the incidence in the unexposed group (Ie - Io).
- Interpreted as the amount of disease incidence among the exposed that is due to the exposure.
Attributable Risk Percent (AR%)
- Calculated as the AR divided by the incidence in the exposed group multiplied by 100.
- Interpreted as the percentage of disease incidence among the exposed that is due to the exposure.
Population Attributable Risk (PAR)
- Calculated as the incidence in the total population minus the incidence in the unexposed group (It - Io).
- Interpreted as the amount of disease incidence in the total population that is due to the exposure.
Population Attributable Risk Percent (PAR%)
- Calculated as the PAR divided by the incidence in the total population multiplied by 100.
- Interpreted as the percentage of disease incidence in the total population that is due to the exposure.
Odds Ratio (OR)
- Calculated as the ratio of the odds of exposure among cases to the odds of exposure among controls.
- Can be used to estimate the RR and AR% in case-control studies.
Estimating AR, AR%, and PAR% from Case-Control Studies
- AR% can be estimated even if Ie and Io are unknown, but only if the OR is a good approximation of the RR.
- PAR% can be estimated when OR is a good approximation of RR, even if Ie and Io are not known.### Estimating PAR% from Case Control Study
- A case control study on lung cancer has 140 cases with 2+ meals cooked/day and 10 cases with 1 meal cooked/day, while the control group has 200 individuals with 2+ meals cooked/day and 50 individuals with 1 meal cooked/day.
Measures of Excess Risk
- Risk ratio (RR) is used to determine if exposure (E) is related to disease (D).
- Odds ratio (OR) is used to determine if exposure (E) is related to disease (D).
- Risk difference (RD) is used to determine if exposure (E) is related to disease (D).
- Attributable risk to the exposed (AR) measures the percentage of the exposed who develop the disease due to exposure.
- Attributable risk percentage (AR%) measures the percentage of cases among the exposed that are due to exposure.
Population Attributable Risk
- Population attributable risk (PAR) measures the percentage of the population that develops the disease due to exposure.
- Population attributable risk percentage (PAR%) measures the percentage of cases in the population that are due to exposure.
Special Excess Risk Measures
- Mortality rate ratio is used to compare mortality rates between groups.
- Mortality rate ratio is calculated as the number of fatal cases divided by the total person-time at risk.
Example of Mortality Rate Ratio
- The age-adjusted heart disease mortality rates in the US from 2000-2014 show a mortality rate ratio of 1.60, indicating that the incidence rate of death from heart disease in males was 60% higher than in females of a similar age.
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Description
Learn to quantify measures of excess risk using incidence rates and estimates, including risk difference, risk ratio, attributable risk, and population attributable risk.
