L1: Introduction and epidemiology part 2 Flashcards
risk and risk ratios?
- she gives more examples this will 100% be in the exam, practice.
risks= Probability of disease developing in an individual in a specified time interval
risked ratio (RR)= The risk ratio (RR) compares the risk of an event (e.g., stroke) in an exposed group vs. an unexposed group. (risk in exposed/risk in unexposed)
pooled risk ratio= Pooled risk ratio is used when you combine data from multiple groups or different populations to estimate a single overall risk ratio. If you combine the data from two different populations, you would calculate the risk ratios separately for each, then pool them to get an overall risk ratio.
This approach is often used in meta-analyses or studies where data from multiple sources are merged. Combining the data allows you to get a more robust estimate of the overall risk, assuming the populations are comparable.
what is a reference level?
Reference level is critical when interpreting a risk ratio. The reference level is typically the unexposed group—this group is considered the “baseline” or the comparison group.
Example: If you have an exposed group (sugary soda drinkers) and an unexposed group (non-soda drinkers), the unexposed group is the reference level.
The risk ratio shows how much more or less risk there is in the exposed group compared to the unexposed (reference) group.
Always state the reference level when interpreting the risk ratio. It’s the group you are comparing against.
it typically has a RR of 1.0
interpreting risk ratio example and confidence intervals?
Risk Ratio of 1 means there is no difference in risk between the two groups.
Risk Ratio > 1 means the exposed group has a higher risk of the event (in this case, stroke).
Risk Ratio < 1 means the exposed group has a lower risk (protective factor).
Interpreting the Risk Ratio Example
Risk Ratio of 1.16: This suggests that people who drink 1 or more servings of sugary soda have a 16% higher risk of having a stroke compared to those who do not drink sugary soda.
Confidence Interval (CI)
The 95% confidence interval (CI) gives a range of values where the true risk ratio likely lies, with 95% confidence that it does not fall outside of this range. Findings are statistically significant when: both lower and upper bound of confidence interval are in the same direction i.e: both above 1 or both below 1 then results are statistically significant
A narrower CI is more precise—it suggests the study has a more reliable estimate of the effect.
If the CI does not include 1 (like 1.01 and 1.34), the result is statistically significant. This means there is a real association between the exposure (sugary soda) and the outcome (stroke). a risk ratio of 0.9 means there is a 10% lower risk of the event in the exposed group. This means the exposed group has 90% of the risk of the unexposed group, or a 10% reduction in risk.
Example:
Confidence Interval of 1.01 and 1.34:
Both values are above 1, indicating an increased risk.
The CI does not include 1, so it is statistically significant.
Confidence Interval including 1, e.g., 1.00 to 1.34:
Borderline significance. The presence of 1 in the CI means no effect is also a possibility, so the result is not certain.
When interpreting a CI, you should mention:
95% probability that the results are not due to chance. 95% probability that findings are not due to chance. Between lower and upper bound of confidence interval
Whether the result is statistically significant (e.g., if the CI does not include 1).
A statement on precision (whether the CI is narrow or wide).
Example of Precision
Narrow CI (e.g., 1.10 to 1.20) → More precise
Wide CI (e.g., 1.01 to 1.34) → Less precise, but still significant if it does not cross 1.
For a Risk Ratio of 0.81 and 0.99:
Both below 1 → Inverse association (protective effect).
Statistically significant because the CI does not include 1.
Narrow CI means high precision.
A confidence interval that does not cross 1 indicates statistical significance.
A narrower CI means better precision, while a wider CI suggests less precision.
Risk ratio not related to public health?
measurements of effect, RR vs absolute risk?
Relative Risk (RR):
This compares the risk of an event (such as developing a disease) in the exposed group versus the unexposed group. It helps to understand the strength of the association between the exposure and the outcome.
It is a relative measure and does not provide direct information on the actual number of people affected.
Example: If a study finds that eating processed meat is associated with a 19% increased risk of bowel cancer:
RR = 1.19 means that those who eat processed meat have a 19% higher chance of developing bowel cancer compared to those who do not.
What does this mean? It shows the relative increase in risk for those who are exposed to processed meat, but does not provide the actual probability of getting bowel cancer.Such Relative risks are known to exaggerate apparent effect
Absolute risk: i.e. incidence, prevalence? Absolute Risk:
This is the actual risk of an event occurring in a population or group over a given period of time. It gives a more concrete sense of how likely an event is in the real world and is easier to understand from a public health perspective.
The absolute risk considers the baseline risk (risk without the exposure) and shows the direct impact of the exposure.
Example: If 6% of people will get bowel cancer anyway (without exposure to processed meat), and the relative risk of eating processed meat increases this by 19%, the absolute risk is calculated as follows:
RR of 1.19 (for the exposed group) × 6% (0.06) baseline risk = 7% absolute risk.
This means that 7% of people who eat processed meat are expected to develop bowel cancer (compared to 6% of the general population). The actual increase is only 1%. One extra case of bowel cancer per 100 people.
Key takeaway: The absolute risk gives the actual likelihood of a person developing bowel cancer due to the exposure (processed meat), not just the relative comparison between exposed and unexposed groups.
Relative- how exposure is related to outcome
Absolute- what actual consequence is in terms of how it effects population. Public health point of view.
