17 Questions
What is the purpose of the 'comparison' in the final proof process?
To measure the extent of association, effect, or risk
What is the significance of Step 1 in establishing an 'exposure - outcome' relationship?
Ensuring the accuracy of study results and avoiding spurious findings
If a study has a non-significant p-value, what is one possible reason ?
Low power of the study (small sample size)
What should an investigator consider if the 'exposure - outcome' association is statistically significant?
Evaluate if the relationship is due to a third variable (confounder)
What is suggested if the exposure-outcome association is not statistically significant?
Use meta-analysis to explore the relationship further
'Validity, reliability, and bias' are factors considered in which step of establishing an exposure - outcome relationship?
Step 1
Which type of association is exemplified by the relationship between shoe size and reading performance in elementary school children?
Spurious association
What is the main purpose of a 'comparison' in observational studies when evaluating associations?
To generate a summary measure of association or risk
In the context of epidemiological studies, what does it mean when we hypothesize that a factor 'may have a role in etiology'?
The factor is a probable contributor to the development of the disease
Which statistical measures are commonly used as the extent of 'Association' or 'Effect' in observational studies?
Risk Ratio (RR) and Odds Ratio (OR)
When evaluating a potential causal relationship between two factors in epidemiology, what should be emphasized before drawing conclusions?
Considering confounding variables and biases
What is the first question that must be asked when an association is observed?
Is it real?
How is bias defined in the context of a study?
A systematic error leading to a mistaken estimate of the exposure's effect
Why is bias considered a systematic error?
Because once introduced, it cannot be fixed
What is the impact of bias on the estimate of an exposure's effect?
Results in an estimate either above or below the true value
How do alternative explanations like bias and confounding affect study results?
They may lead to spurious results
When observing an association, what might bias or confounding lead researchers to falsely conclude?
Presence of a valid association when there isn't one
Study Notes
Bias and Confounding
- Bias is a systematic error in the design, conduct, or analysis of a study that results in a mistaken estimate of an exposure's effect on the risk of disease.
- Bias can produce spurious results, leading to conclusions of a valid statistical association when none exists or vice versa.
- The effect of bias will be an estimate either above or below the true value.
Establishing a Cause & Effect Relationship
- The process of establishing a cause & effect relationship involves a sequence of steps.
- Step 1: Ensure the results of the study are accurate and not spurious, considering correct methods, validity, reliability, and bias.
- Step 2a: Determine if statistical results indicate an association, using p-value and 95% CI.
- Step 2b: If not significant, consider the possibility of low power due to a small sample size, and suggest additional studies or meta-analysis.
- Step 3: Evaluate if the relationship is due to an indirect relationship with a third variable (confounder).
- Step 4: If the confounder is excluded, test the postulated causal relationship on the criteria of causal association.
Association and Causation
- Association is the concurrence of two variables more often than would be expected by chance.
- Types of associations include spurious, indirect, direct (causal), one-to-one causal, and multi-factorial causal.
- Observing an association does not necessarily imply causation; a comparison is required to establish a causal relationship.
Examples of Association and Causation
- High serum homocysteine levels may be associated with an increased risk of IHD, but further comparison is needed to establish a causal relationship.
- The presence of Helicobacter pylori may be associated with duodenal ulcers, but further comparison is needed to establish a causal relationship.
Test your knowledge on the concepts of association and causation in epidemiological studies, as discussed by Dr. Sireen Alkhaldi in the field of community medicine for the academic years 2023/2024 at the School of Medicine, The University of Jordan.
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