Epidemiology Lecture 4: Study Designs and Bias

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Questions and Answers

What is required for studying rare outcomes effectively?

A large cohort and long follow-up period (correct)

A small cohort and short follow-up period

Randomized controlled trial only

Multiple studies with varying designs

What association was identified in the study by Freeman et al. regarding HSV-2 infection?

Three times higher risk of HIV acquisition (correct)

No increased risk of HIV acquisition

Significantly lower risk of HIV acquisition

Double risk of HIV acquisition

What limitation did the study identify that may affect the interpretation of the association between HSV-2 and HIV acquisition?

Inaccurate measurement of HSV-2 infection

Unmeasured confounders like sexual behavior (correct)

Insufficient sample size

Excessively long follow-up period

Why is one study rarely sufficient to influence policy decisions?

It often takes a wide range of studies over many years to accumulate evidence (B) Signup and view all the answers

What factor can lead to different conclusions in studies addressing the same questions?

Measurement definitions and study designs (D) Signup and view all the answers

What does Type 1 error refer to?

Accepting a new treatment that has no actual effect. (B) Signup and view all the answers

What is the common significance level set to control Type 1 error?

0.05 (B) Signup and view all the answers

Which of the following best describes a Type 2 error?

Failing to find a significant relationship that actually exists. (D) Signup and view all the answers

How can the power of a study be increased?

Increasing sample sizes and effect sizes. (C) Signup and view all the answers

What is the primary issue caused by selection bias in a study?

Participants are not representative of the target population (C) Signup and view all the answers

What is meant by random error?

Error resulting from chance affecting precision. (D) Signup and view all the answers

Which of the following describes confounding in research?

When an extraneous variable distorts the relationship being studied. (B) Signup and view all the answers

Which of the following is a mitigation strategy for reporting bias?

Preregistration of studies (A) Signup and view all the answers

What can mitigate information bias in a study?

Randomization of participants. (B) Signup and view all the answers

Which bias occurs when incorrect conclusions are drawn from a study's results?

Bias of inference (D) Signup and view all the answers

What is an example of information bias?

People with a disease remembering their past exposures better. (C) Signup and view all the answers

What does publication bias suggest about the types of studies more likely to be published?

Studies with significant findings are overrepresented (A) Signup and view all the answers

What is a common method to mitigate selection bias in research studies?

Implementing random sampling techniques (B) Signup and view all the answers

What is a primary disadvantage of ecological studies?

They may suffer from confounding factors. (C) Signup and view all the answers

Which factor does NOT contribute to bias of inference in research?

Drawing conclusions from a large, diverse sample (A) Signup and view all the answers

Which of the following best describes cross-sectional studies?

They collect data at a single point in time. (A) Signup and view all the answers

What is a significant limitation of case-control studies?

They are not effective for studying multiple exposures. (D) Signup and view all the answers

When conducting ecological studies, what is primarily compared?

Aggregated population statistics of exposures and outcomes (D) Signup and view all the answers

What effect does confirmation bias have on research outcomes?

Limiting the exploration of contradictory evidence (D) Signup and view all the answers

What is one of the advantages of cross-sectional studies?

They are quick to conduct and can investigate many variables. (A) Signup and view all the answers

Why might ecological studies generate hypotheses?

They utilize existing data from diverse populations. (D) Signup and view all the answers

What can case-control studies not be used to estimate?

Prevalence of the disease. (C) Signup and view all the answers

What is a key characteristic of cross-sectional studies regarding health outcomes?

They measure the prevalence of health outcomes. (B) Signup and view all the answers

What is a common misconception about case-control studies?

They are ideal for studying multiple outcomes. (D) Signup and view all the answers

What is the primary goal of epidemiology?

To identify and understand health problems in populations (A) Signup and view all the answers

Which of the following is NOT a type of observational study design in epidemiology?

Randomised controlled trial (B) Signup and view all the answers

What does the null hypothesis (H0) assume in statistical testing?

There is no effect or association between variables (D) Signup and view all the answers

Which statement describes a Type 1 Error in epidemiological research?

Identifying an effect when none exists (C) Signup and view all the answers

What is typically quantified in epidemiological research to explore associations?

Exposure, outcome, and confounders (A) Signup and view all the answers

Which of the following study designs uses interventions to analyze outcomes?

Randomised controlled trial (B) Signup and view all the answers

What is a common question addressed in epidemiological studies?

What correlation exists between exposure and health outcomes? (B) Signup and view all the answers

What type of study compares outcomes at a single point in time?

Cross-sectional study (D) Signup and view all the answers

What is a significant challenge in determining the causality of severe pneumonia in children?

Recall bias may influence parents' responses. (A) Signup and view all the answers

What does a cohort study primarily investigate?

The time sequence of exposure leading to an outcome over time. (D) Signup and view all the answers

Which is a known advantage of cohort studies?

They can measure incidence rates of health outcomes. (C) Signup and view all the answers

Which factor could lead to selection bias in cohort studies?

High attrition rates during follow-up. (D) Signup and view all the answers

What is one of the main limitations of the PERCH study design?

Difficulty in establishing whether cases and controls come from comparable populations. (B) Signup and view all the answers

What could influence the ascertainment of outcomes in cohort studies?

Knowledge of exposure status by researchers. (D) Signup and view all the answers

What has been observed regarding the prevalence of viruses among pneumonia cases in the PERCH study?

Viruses like RSV were more common in cases than anticipated. (C) Signup and view all the answers

Which of the following statements best describes the limitation of cohort studies regarding exposure status?

Individuals may be misclassified due to changing diagnostic protocols. (C) Signup and view all the answers

Study Notes

Lecture 4: Study Designs and Bias Sources in Epidemiology

Epidemiology is the study of the distribution and determinants of health or disease in populations, and the application of this knowledge to control health problems.
Epidemiological questions include what's causing a particular disease in a population, the average risk of disease, who is most at risk, and how risk can be reduced.
A major goal is to explain patterns of disease occurrence and causation (etiology).
Other questions include determining if there's an association between an exposure and outcome, if an exposure is the cause of the outcome/disease, and how much an exposure increases the risk.
Epidemiological research aims to quantify exposure, outcome, and confounders.
Different study designs are used to evaluate the association between an exposure and outcome.

Study Designs in Epidemiology

Observational studies:
- Ecological
- Cross-sectional
- Case-control
- Cohort
Intervention/Experimental studies:
- Randomized controlled trials
- Intervention/non-experimental
- Difference-in-Difference, IV, ITS

Null Hypothesis

The null hypothesis (H0) is a statement assuming no effect, association, or difference between groups/variables in statistical testing.
It serves as the default assumption, and if evidence supports rejecting it, the alternative hypothesis (H1) is considered.

Type 1 and Type 2 Errors

Type 1 Error (False Positive): Concluding an effect or association exists when none exists.
Example: Concluding a new drug is effective when it's not.
Significance Level (α): The probability of making a Type 1 error (commonly set at 0.05)
Type 2 Error (False Negative): Failing to detect an effect or association that truly exists.
Example: Concluding a drug doesn't lower blood pressure when it actually does.
Power (1-β): Probability of avoiding a Type 2 error. Increased sample size and effect size increase power.

Bias

Causal Effect: Random Error, Confounding
Information Bias (misclassification)
Selection bias
Bias in inference
Reporting bias
Bias in knowledge use

Explanation of Biases

Random Error: Arises from chance, affects precision, leads to variability in data, but doesn't favor one outcome over another.
Example: Measuring blood pressure multiple times with different results.
Mitigation: Increasing sample size, averaging multiple measurements.
Confounding: An extraneous variable associated with both the exposure and outcome, distorting the relationship.
Example: Studying alcohol consumption and lung cancer without accounting for smoking.
Mitigation: Randomization, matching, stratification, or multivariable analysis.
Information Bias: Errors in measuring exposure, outcome, or other variables leading to misclassification.
Example: Recall bias in case-control studies.
Mitigation: Using objective measures and blinding data collection.
Selection Bias: Participants in a study aren't representative of the target population due to how they're selected.
Example: Recruiting participants for a study from fitness centers only.
Mitigation: Ensuring random sampling & minimizing loss to follow-up.
Bias of Inference: Drawing incorrect conclusions from a study due to overgeneralization or ignoring limitations.
Example: Concluding a drug is effective for all populations based on results from a small, homogenous sample.
Mitigation: Carefully interpreting results and acknowledging limitations.
Reporting Bias: Selection of results for reporting, typically favorable ones.
Example: Reporting only the positive outcomes of a new drug.
Mitigation: Preregistration of studies, requiring full reporting.
Publication bias: Studies with positive results are more likely to be published than those with negative or null results.
Example: Meta-analyses may overestimate treatment effects if only published studies are included.
Mitigation: Encouraging publication of all results and use of trial registries to identify unpublished data.

Ecological Studies

Compare overall population or group statistics of exposures and outcomes.
Aggregated level; exposure prevalence arrow outcome prevalence
Example: Average diet and life expectancy across multiple countries.
Advantages: Cheap & quick, generate hypotheses
Disadvantages: Difficult to draw conclusions at the individual level (ecological fallacy), populations can differ in other ways.

Cross-Sectional Studies

Measure all factors (exposure, outcome, confounders) at one time point.
Used to measure prevalence of health outcomes & describe features of a population.
Don't follow individuals over time.
Advantages: Quick
Disadvantages: Time sequence of events difficult to ascertain, only measure prevalence, large surveys needed for rare diseases.

Case-Control Studies

Identify people with a health outcome (cases) & select appropriate controls.
Compare the proportion exposed between cases and controls.
Example: Vaccine effectiveness studies.
Advantages:Investigate multiple exposures (one outcome); relatively quick; good for rare outcomes (e.g., cancers)
Disadvantages: limited to one outcome; selection bias if controls not comparable to cases; difficult to determine time sequence of events.

Cohort Studies

Follow a group of people over time according to their exposure status to see who develops a health outcome.
Example: Analyze association between talc powder use & ovarian cancer.
Advantages: Measure incidence, time sequence clear, rare exposures can be studies; multiple exposures and outcomes
Disadvantages: often time-consuming & expensive, losses to follow-up (selection bias); outcome may be influenced by knowledge of exposure.

Summary

Study design is crucial for valid conclusions.
Multiple studies over time often needed for evidence to influence policy.
Study designs can vary, affecting conclusions.
Factors such as the definition/measurement of exposure/outcome, biases in the selection of participants, how confounders are measured, and differences in the populations studied are important considerations.
Important to interpret findings in relation to the study design.

Studying That Suits You

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Description

Dive into the fundamental study designs used in epidemiology and explore the sources of bias that can affect research outcomes. This quiz covers observational studies, interventional studies, and important concepts related to causation and risk assessment in population health. Test your knowledge of how these methodologies contribute to understanding disease patterns.