Epidemiology Study Designs
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Questions and Answers

What is a major limitation of cross-sectional studies?

  • Recall bias
  • Lack of random assignment to exposure groups
  • Time-consuming and expensive
  • Only assessing one outcome (correct)

    • What is a strength of observational studies?

  • Recall bias is eliminated
  • Random assignment to exposure groups
  • Ability to establish causation
  • Can study any question, including harmful exposures (correct)

    • What is a key consideration when appraising the quality of an observational study?

  • The size of the study population
  • The use of a randomized design
  • The consideration of confounding factors (correct)
  • The use of a control group

    • What is a characteristic of systematic reviews?

    <p>They use explicit and rigorous methods to identify and critically appraise studies</p> Signup and view all the answers

    What is a limitation of observational studies?

    <p>They are not randomly assigned to exposure groups</p> Signup and view all the answers

    What is a characteristic of cross-sectional studies?

    <p>They compare current disease status and current exposure</p> Signup and view all the answers

    What is a limitation of systematic reviews?

    <p>They are only as good as the available studies</p> Signup and view all the answers

    What is a strength of N of 1 studies?

    <p>They allow for individualization and root-cause style treatment</p> Signup and view all the answers

    What is a limitation of preclinical studies?

    <p>They are not generalizable to humans</p> Signup and view all the answers

    What is an advantage of meta-analysis?

    <p>It allows for the creation of a larger sample size</p> Signup and view all the answers

    What is a characteristic of a strong systematic review?

    <p>It uses a comprehensive search strategy</p> Signup and view all the answers

    What is a limitation of N of 1 studies?

    <p>They do not work for curable or self-limiting conditions</p> Signup and view all the answers

    What is a strength of preclinical studies?

    <p>They allow for a high level of control over the experimental conditions</p> Signup and view all the answers

    What is a consideration when evaluating evidence from preclinical studies?

    <p>Is the evidence sufficient to guide clinical recommendations?</p> Signup and view all the answers

    What is the primary concern of 'imprecision' in assessing the risk of bias in individual studies?

    <p>The results are due to chance</p> Signup and view all the answers

    What is the main purpose of a forest plot in assessing the risk of bias in individual studies?

    <p>To assess inconsistency</p> Signup and view all the answers

    What would increase the certainty of evidence in a study?

    <p>A large magnitude of effect</p> Signup and view all the answers

    What is the concern of 'indirectness' in assessing the risk of bias in individual studies?

    <p>The intervention is not studied in the population of interest</p> Signup and view all the answers

    What is the purpose of GRADE in assessing the risk of bias in individual studies?

    <p>To assess the body of evidence as a whole</p> Signup and view all the answers

    What is the main concern of 'publication bias' in assessing the risk of bias in individual studies?

    <p>Only positive results are published</p> Signup and view all the answers

    What is the concern of 'inconsistency' in assessing the risk of bias in individual studies?

    <p>The results of individual studies are inconsistent</p> Signup and view all the answers

    What is the primary concern of 'risk of bias' in assessing individual studies?

    <p>Systematic errors in the study design</p> Signup and view all the answers

    What is the primary goal of intention to treat analysis in RCTs?

    <p>To minimize bias from dropouts</p> Signup and view all the answers

    Which type of method is used to assess compliance in RCTs?

    <p>Both biological and simple methods</p> Signup and view all the answers

    What is a limitation of per-protocol analysis?

    <p>It is susceptible to bias from dropouts</p> Signup and view all the answers

    Why is it difficult to conduct RCTs?

    <p>Because of the difficulty in minimizing bias</p> Signup and view all the answers

    What is a benefit of intention to treat analysis?

    <p>It provides a cautious, underestimation of the effect size</p> Signup and view all the answers

    What is a common issue in RCTs that can lead to bias?

    <p>Systematic factors impacting withdrawals</p> Signup and view all the answers

    What is a technique used in intention to treat analysis to handle missing data?

    <p>Last observation carried forward</p> Signup and view all the answers

    Why is per-protocol analysis not recommended?

    <p>Because it is susceptible to bias from dropouts</p> Signup and view all the answers

    What is the primary concern of 'imprecision' when assessing the risk of bias in individual studies?

    <p>The results are due to chance</p> Signup and view all the answers

    What is the purpose of a funnel plot in assessing the risk of bias in individual studies?

    <p>To detect publication bias</p> Signup and view all the answers

    What is the concern of 'inconsistency' in assessing the risk of bias in individual studies?

    <p>The studies show varying results</p> Signup and view all the answers

    What is the key consideration when rating the certainty of evidence down due to indirectness?

    <p>The intervention of interest was not studied in the population of interest</p> Signup and view all the answers

    What increases the certainty of evidence in a study?

    <p>A large magnitude of effect</p> Signup and view all the answers

    What is the purpose of GRADE in assessing the risk of bias in individual studies?

    <p>To assess the body of evidence as a whole</p> Signup and view all the answers

    What would decrease the certainty of evidence in a study?

    <p>Few observed events or few participants</p> Signup and view all the answers

    What is the concern of 'publication bias' in assessing the risk of bias in individual studies?

    <p>Only small studies that confirm investigators' perceptions are available</p> Signup and view all the answers

    What is a major advantage of cross-sectional studies?

    <p>They are faster and can study rare outcomes.</p> Signup and view all the answers

    What is a key limitation of observational studies?

    <p>They are not randomly assigned to exposure groups.</p> Signup and view all the answers

    What is an important consideration when appraising the quality of an observational study?

    <p>Was the assessment of exposure accurate and validated?</p> Signup and view all the answers

    What is a key characteristic of systematic reviews?

    <p>They use explicit and rigorous methods to identify and appraise studies.</p> Signup and view all the answers

    What is a potential source of bias in observational studies?

    <p>Selection bias.</p> Signup and view all the answers

    What is a key consideration when evaluating the quality of an observational study?

    <p>Did the study consider confounding factors?</p> Signup and view all the answers

    What is the primary goal of the GRADE framework?

    <p>To develop a systematic approach to clinical decision making</p> Signup and view all the answers

    What does a high certainty rating in the GRADE framework indicate?

    <p>The authors believe that the true effect is probably close to the estimated effect</p> Signup and view all the answers

    What is an example of a risk of bias in a study?

    <p>An inherent limitation in the design of a study</p> Signup and view all the answers

    What is the purpose of informing patients about the risks and benefits of a treatment?

    <p>To obtain informed consent</p> Signup and view all the answers

    What is the purpose of considering alternatives in clinical decision making?

    <p>To ensure that patients are aware of all possible options</p> Signup and view all the answers

    What is the purpose of monitoring patient response in clinical decision making?

    <p>To alter treatment if needed</p> Signup and view all the answers

    What is the purpose of grading the evidence in clinical decision making?

    <p>To evaluate the quality of the evidence</p> Signup and view all the answers

    What is the main concern of publication bias in assessing the risk of bias in individual studies?

    <p>Only positive results are published</p> Signup and view all the answers

    What is the main purpose of considering the factors of consistency, precision, and applicability in a study?

    <p>To evaluate the quality of the evidence</p> Signup and view all the answers

    A recommendation is considered weak when:

    <p>There is variation in the decision made by informed people</p> Signup and view all the answers

    What is the primary purpose of a GRADE-assessed systematic review and meta-analysis?

    <p>To summarize the effects of an intervention on a particular outcome</p> Signup and view all the answers

    In the context of a recommendation, what is 'equity' a consideration of?

    <p>The distribution of the benefits and harms of an intervention among different populations</p> Signup and view all the answers

    What is the main difference between a strong and a weak recommendation?

    <p>The variation in the decision made by informed people</p> Signup and view all the answers

    What is the purpose of considering the 'resources' in the context of a recommendation?

    <p>To decide on the feasibility of an intervention</p> Signup and view all the answers

    What is the main purpose of a systematic review and meta-analysis?

    <p>To summarize the effects of an intervention on a particular outcome</p> Signup and view all the answers

    What is the significance of a weighted mean difference (WMD) in a meta-analysis?

    <p>It is a measure of the effect size of an intervention</p> Signup and view all the answers

    What is the focus of GRADE when assessing the risk of bias in individual studies?

    <p>The body of evidence as a whole</p> Signup and view all the answers

    What is the concern of 'indirectness' in assessing the risk of bias in individual studies?

    <p>The intervention was not studied in the population of interest</p> Signup and view all the answers

    What is the primary concern of 'inconsistency' in assessing the risk of bias in individual studies?

    <p>Many similar studies showing a consistent effect</p> Signup and view all the answers

    What is the purpose of a funnel plot in assessing the risk of bias in individual studies?

    <p>To assess publication bias</p> Signup and view all the answers

    What would increase the certainty of evidence in a study?

    <p>A large magnitude of effect</p> Signup and view all the answers

    What is the primary advantage of meta-analysis?

    <p>It allows for the creation of a larger sample size.</p> Signup and view all the answers

    What is a limitation of N of 1 studies?

    <p>They are not suitable for studying curable or self-limiting conditions.</p> Signup and view all the answers

    What is the primary concern of 'imprecision' in assessing the risk of bias in individual studies?

    <p>Few events were observed</p> Signup and view all the answers

    What is the purpose of GRADE in assessing the risk of bias in individual studies?

    <p>To assess the body of evidence as a whole</p> Signup and view all the answers

    What is a strength of preclinical studies?

    <p>They allow for the investigation of the mechanism of action.</p> Signup and view all the answers

    What is a limitation of systematic reviews?

    <p>They are only as good as the available studies.</p> Signup and view all the answers

    What is the primary goal of the GRADE framework?

    <p>To rate the certainty of evidence</p> Signup and view all the answers

    What is the primary purpose of a comprehensive search in a systematic review?

    <p>To identify the most relevant studies.</p> Signup and view all the answers

    What is a consideration when evaluating evidence from preclinical studies?

    <p>Is the study generalizable to humans?</p> Signup and view all the answers

    What is the primary advantage of N of 1 studies?

    <p>They allow for the study of individualized treatments.</p> Signup and view all the answers

    What is a limitation of using preclinical evidence to guide clinical recommendations?

    <p>It may not be generalizable to humans.</p> Signup and view all the answers

    What is the main purpose of considering evidence, benefits/harms, equity, resources, feasibility, and acceptability in making a recommendation?

    <p>To weigh the pros and cons of an intervention</p> Signup and view all the answers

    What is a characteristic of a weak recommendation?

    <p>It is likely to result in varying decisions among informed individuals</p> Signup and view all the answers

    What is the purpose of conducting a systematic review and meta-analysis?

    <p>To summarize the effects of an intervention on a specific outcome</p> Signup and view all the answers

    What is the benefit of using the GRADE framework in assessing the risk of bias in individual studies?

    <p>It provides a standardized approach to rating the certainty of evidence</p> Signup and view all the answers

    What is a characteristic of a strong recommendation?

    <p>It is likely to result in consistent decisions among informed individuals</p> Signup and view all the answers

    What is the primary goal of shared decision making in the context of recommendations?

    <p>To promote patient-centered care</p> Signup and view all the answers

    What is the benefit of considering the baseline characteristics of participants in a systematic review and meta-analysis?

    <p>It enables subgroup analysis and identification of specific effects</p> Signup and view all the answers

    What is the purpose of blinding in a study?

    <p>To remove expectation</p> Signup and view all the answers

    What is an example of a confounding factor?

    <p>Age</p> Signup and view all the answers

    What is the purpose of clearly defining a population in a study?

    <p>To improve generalizability</p> Signup and view all the answers

    What can influence the sample in a study?

    <p>Recruitment method</p> Signup and view all the answers

    What is an important aspect of reporting results in a study?

    <p>Reporting the power calculation</p> Signup and view all the answers

    Why are certain populations often excluded from clinical trials?

    <p>Due to potential confounding factors</p> Signup and view all the answers

    What is the primary goal of the GRADE framework?

    <p>To provide a systematic approach to clinical decision making</p> Signup and view all the answers

    What does a 'high' certainty rating in the GRADE framework indicate?

    <p>The authors have a lot of confidence that the true effect is similar to the estimated effect</p> Signup and view all the answers

    What is an example of a risk of bias in a study?

    <p>Inherent limitation in the design of a study</p> Signup and view all the answers

    What is the purpose of informing patients about the risks and benefits of a treatment?

    <p>To obtain informed consent</p> Signup and view all the answers

    What is the purpose of considering alternatives in clinical decision making?

    <p>To weigh the benefits and risks of different treatment options</p> Signup and view all the answers

    What is the purpose of monitoring patient response in clinical decision making?

    <p>To alter treatment if needed</p> Signup and view all the answers

    Why is it important to evaluate the quality of evidence in clinical decision making?

    <p>To ensure that the evidence is relevant to the patient's condition</p> Signup and view all the answers

    What is the purpose of a systematic review in evaluating evidence?

    <p>To provide an estimate of the effect size of an outcome</p> Signup and view all the answers

    What is the primary purpose of a surrogate outcome in a clinical study?

    <p>To provide an early indication of the effect of an intervention on a clinical outcome</p> Signup and view all the answers

    What does an odds ratio of 1 indicate in a clinical study?

    <p>The exposure has no effect on the outcome</p> Signup and view all the answers

    What is a common issue with surrogate outcomes?

    <p>They may not be validated</p> Signup and view all the answers

    What is the primary difference between clinical significance and statistical significance?

    <p>Clinical significance refers to the effect size, while statistical significance refers to the p-value</p> Signup and view all the answers

    What is the purpose of power in a clinical study?

    <p>To detect a real difference between two groups</p> Signup and view all the answers

    What is an example of a clinical outcome?

    <p>Stroke</p> Signup and view all the answers

    What does a p-value of less than 0.05 indicate in a clinical study?

    <p>The observed effect is statistically significant</p> Signup and view all the answers

    What is a limitation of using surrogate outcomes in clinical studies?

    <p>They may not be correlated with the true outcome</p> Signup and view all the answers

    What is the primary reason why a non-significant difference may be found in a study?

    <p>The study is underpowered to detect a difference</p> Signup and view all the answers

    What is the relative risk reduction in the example where the event rate is 12% in the treatment group and 20% in the control group?

    <p>40%</p> Signup and view all the answers

    What is the absolute risk reduction in the example where the event rate is 12% in the treatment group and 20% in the control group?

    <p>8%</p> Signup and view all the answers

    Why may a large difference be seen between the absolute risk reduction and the relative risk reduction when the outcome occurs infrequently?

    <p>Because the outcome is rare</p> Signup and view all the answers

    What is the primary goal of hypothesis testing in statistics?

    <p>To decide whether the findings of an investigation reflect chance or a real effect</p> Signup and view all the answers

    What is the purpose of the odds ratio in a study?

    <p>To examine the relationship between an exposure and an outcome</p> Signup and view all the answers

    What is the difference between incidence and prevalence?

    <p>Incidence is the number of new cases, while prevalence is the total number of cases</p> Signup and view all the answers

    What is the scenario where the intervention reduces the risk from 4% to 3%?

    <p>A 25% relative risk reduction</p> Signup and view all the answers

    What is the significance of the p-value of 0.055 in the example comparing the hemoglobin A1c levels in two groups?

    <p>The difference is not statistically significant</p> Signup and view all the answers

    What is the purpose of a 95% confidence interval?

    <p>To provide a range of values within which the true result is likely to lie</p> Signup and view all the answers

    What is the interpretation of a p-value of 0.03?

    <p>The result is significant, as the p-value is less than 0.05</p> Signup and view all the answers

    What is the implication of a 50% relative risk reduction in the risk of SIDS with pacifier use?

    <p>The risk of SIDS decreases from 0.00004% to 0.00002% per 100,000</p> Signup and view all the answers

    What is the difference between a sample and a population?

    <p>A sample is a subset of the group, while a population is the entire group of people</p> Signup and view all the answers

    What is the purpose of calculating the number needed to treat?

    <p>To determine the effectiveness of a treatment</p> Signup and view all the answers

    What is the difference between absolute and relative risk?

    <p>Absolute risk is the difference in risk between two groups, while relative risk is the ratio of the risk in one group to the risk in another group</p> Signup and view all the answers

    What is the purpose of calculating the odds ratio?

    <p>To determine the strength of association between a risk factor and an outcome</p> Signup and view all the answers

    Study Notes

    Cross-Sectional Studies

    • Compare current disease status and current exposure
    • Strengths: Can study rare outcomes, faster, and no recall bias
    • Weaknesses: Assignment to comparison group is not random, no assessment of temporality, and only assessing one outcome

    Observational Studies

    • Can study any question, less expensive or faster than intervention studies
    • Limitations: Not randomly assigned to exposure groups, investigate correlation, not necessarily causation

    Appraising the Quality of Observational Studies

    • Recruitment: Do participants reflect the population of interest? (Selection Bias)
    • Assessment of exposure: accurate, subjective or objective, validated, and measurement or classification bias
    • Consideration of confounding factors

    Systematic Reviews

    • Strengths: Explicit and rigorous methods, scientific investigation with pre-planned methodology, enormous effort to minimize bias, capture the big picture of evidence on a topic, and meta-analysis allows for a larger sample size
    • Limitations: Only as good as the available studies, publication bias, lack of research on a topic, and can't replace good clinical reasoning

    What Makes a Strong Systematic Review?

    • Clear question
    • Comprehensive search
    • Assessment of study quality

    N of 1 Study

    • Strengths: Look at real-world use of an intervention, allows for individualization, and compare naturopathic and conventional treatments
    • Limitations: Doesn't work if the condition is curable or self-limiting, findings may not be generalizable, ethics, and high cost

    Preclinical Studies

    • Strengths: Allow for creativity and innovation, study possible adverse events or interactions, and high level of control
    • Limitations: May not be clinically applicable to humans, highly controlled, and one isolated part of the story

    Considerations

    • Is pre-clinical evidence sufficient to guide clinical recommendations?
    • Assessing risk of bias in individual studies and the body of evidence as a whole

    GRADE Framework

    • Imprecision: Are the results due to chance? Focus on 95% confidence interval
    • Inconsistency: Many similar studies showing a consistent effect increase certainty
    • Indirectness: Certainty is downrated when the intervention of interest is not studied in the population of interest and reporting the outcome of interest
    • Publication Bias: Is this really all of the research evidence that exists?

    What Makes Evidence More Certain?

    • Large magnitude of effect
    • Dose-response gradient
    • All residual confounding would increase our confidence in an effect
    • Ex. A very large observational or non-randomized study without other limitations

    Compliance

    • Should be assessed using simple methods like diary, pill count, phone calls, and questioning, or biological methods like blood/urine levels (although costly)

    Withdrawals

    • Important to account for missing data, with two approaches:
      • Per-protocol analysis: only analyzes people in the intervention group who completed the study
      • Intention to treat analysis: analyzes everyone in the group they were randomized to, even if they didn't complete or ended up in the other group

    Risk of Per-Protocol Analysis

    • Can lead to biased results due to systematic factors impacting who drops out (e.g., side effects, acceptability, impact on outcome)

    Intention to Treat Analysis

    • Techniques: last observation carried forward, statistical approaches
    • Best way to minimize bias from dropouts
    • Cautious, under-estimates effect (vs. per-protocol analysis, which over-estimates effect)

    RCT Limitations

    • Difficult to recall bias
    • Only assessing one outcome
    • Participants may not be representative of the population

    Cross-Sectional Studies

    • Compare current disease status and current exposure
    • Strengths: can study rare outcomes, faster, no recall bias
    • Weaknesses: assignment to comparison group is not random, no assessment of temporality, only assessing one outcome

    Observational Studies

    • Strengths: can study any question, less expensive or faster than intervention studies
    • Limitations: not randomly assigned to exposure groups, investigate correlation, not causation

    Appraising Quality of Observational Studies

    • Recruitment: do participants reflect the population of interest? (selection bias)
    • Assessment of exposure: accurate? (measurement or classification bias)
    • Consideration of confounding factors?

    Systematic Reviews

    • Explicit and rigorous methods to identify, critically appraise, and synthesize evidence
    • Informed consent, consider alternatives, monitor patient response and safety, alter treatment if needed

    Grading the Evidence

    • GRADE (Grading of Recommendations, Assessment, Development, and Evaluations) framework
    • Transparent framework for developing and presenting summaries of evidence
    • Systematic approach to clinical decision making

    How GRADE Works

    • Clinical question (PICO format)
    • Systematic review provides an estimate of the effect size of an outcome
    • Author rates the quality of the evidence and strength of recommendations

    GRADE Certainty Rating

    • Certainty: whether an estimate of association or effect is correct or true
    • Five levels of certainty: very low, low, moderate, high, and very high

    What Makes Evidence Less Certain?

    • Risk of bias
    • Imprecision
    • Inconsistency
    • Indirectness
    • Publication bias

    What Makes Evidence More Certain?

    • Large magnitude of effect
    • Dose-response gradient
    • All residual confounding would increase confidence in an effect
    • Large observational or non-randomized studies without other limitations

    GRADE: 2 Parts

    • Certainty of Evidence
    • Recommendation Strength
      • Consider evidence, benefits/harms, equity, resources, feasibility, acceptability

    Selection Bias

    • Sample confounding factors: age, gender, family history, comorbidities, BMI, socioeconomic status, marital status, education, exercise, diet, and other known or unknown factors
    • Blinding: removes expectation bias; types of blinding include single blinding (participants), double blinding (person delivering the intervention), and triple blinding (person assessing the outcome)
    • Clearly defined population: participants are a sample of a larger population; inclusion and exclusion criteria help define the population; consider generalizability (e.g., more or less ill, different ethnicity or geographic location)

    Bias in Measurement of Outcomes

    • Reporting of results: includes power calculation, reporting of planned measurements, and consideration of missing data and p-values
    • Systematic review: a scientific investigation with pre-planned methodology to minimize bias; allows for the creation of a larger sample size and captures the big picture of evidence on a topic
    • Limitations of systematic review: only as good as the available studies; can't replace good clinical reasoning

    N of 1 Study

    • Strengths: looks at real-world use of an intervention; allows for individualization and comparison of naturopathic and conventional treatments
    • Limitations: doesn't work if the condition is curable or self-limiting; findings may not be generalizable; high cost and ethical concerns

    Preclinical Study

    • Strengths: allows for creativity and innovation; investigates mechanism of action; studies possible adverse events or interactions
    • Limitations: may not be clinically applicable to humans; highly controlled; only one isolated part of the story

    Grading the Evidence

    • GRADE: a transparent framework for developing and presenting summaries of evidence; systematic approach to clinical decision making
    • Grading of evidence: considers certainty of effect, imprecision, inconsistency, indirectness, and publication bias
    • Recommendation strength: considers evidence, benefits/harms, equity, resources, feasibility, and acceptability

    Certainty of Evidence

    • Risk of bias: bias in individual studies; many tools for assessing risk of bias
    • Imprecision: are the results due to chance? Focuses on 95% confidence interval
    • Inconsistency: compares results of individual studies; looks at forest plots and statistical heterogeneity
    • Indirectness: considers if the intervention was studied in the population of interest and reported the outcome of interest
    • Publication bias: considers if all relevant studies were included; uses visual and statistical methods for assessment

    What Makes Evidence More Certain?

    • Large magnitude of effect
    • Dose-response gradient
    • All residual confounding would increase confidence in an effect
    • Ex. A very large observational or non-randomized study without other limitations

    GRADE: 2 Parts

    • Certainty of evidence: how likely is it that something works?
    • Recommendation strength: should it be recommended for use? Consider evidence, benefits/harms, equity, resources, feasibility, and acceptability

    Statistics

    • Define terms: sample, population, incidence, prevalence, and power

    Population vs Sample

    • Population: entire group of interest
    • Sample: subset of population for study

    Prevalence and Incidence

    • Prevalence: total number of cases suffering from a disorder (e.g. 26,630 HIV-positive persons in Ontario in 2008)
    • Incidence: number of new cases suffering from a disorder (e.g. 1,620 new HIV infections in Ontario in 2008, ~0.0001 or 1 in 10,000)

    Hypothesis Testing

    • Process of deciding whether study findings reflect chance or real effect
    • Involves:
      • Difference in group means (averages)
      • Difference in likelihood of an outcome
      • Statistical significance (real differences or chance?)

    Statistical Significance: P-Value

    • P-value: probability of difference being due to chance
    • Generally, 0.05 is the cut-off (5% likelihood)
    • If p > 0.05, not significant; if p < 0.05, significant

    Statistical Significance: CI

    • 95% Confidence Interval (CI): range of values within which the true result is likely to lie
    • If CI intervals overlap, non-significant difference; if they don't, significantly different

    Relative Risk

    • Probability of a bad outcome in the intervention group divided by probability of a bad outcome in the control group
    • RR = 1: no difference; RR > 1: increased risk; RR < 1: decreased risk

    Relative Risk Reduction

    • How much did the treatment reduce the risk of the bad outcome?
    • RRR = 1 - relative risk

    Absolute vs Relative Risk Reduction

    • Absolute RR: absolute amount the intervention decreased the risk
    • ARR = risk of outcome with placebo - risk with mediation
    • ARR and RRR can be misleading when outcomes occur infrequently

    Odds Ratio

    • Measures the relationship between an exposure and an outcome
    • Often used in observational studies
    • OR = 1: exposure does not affect the likelihood of the outcome; OR > 1: exposure associated with increased likelihood of the outcome

    Outcomes

    • Clinical outcomes: actual events or conditions (e.g. stroke, suicide, hip fracture)
    • Surrogate outcomes: indicators of disease progression, not clinical events (e.g. biomarkers, LDL-Cholesterol, Columbia Suicide Severity Scale)
    • Surrogate outcomes must be validated to ensure they predict the true outcome

    Clinical Significance

    • Does the intervention have a genuine, measurable effect?
    • Related to extent of change and whether it makes a real difference in patients' lives
    • No broadly accepted standard for clinical significance

    Power

    • Ability of a study to detect a real difference between two groups
    • Depends on sample size, ability to detect differences, and extent of change

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    Description

    This quiz covers the characteristics of cross-sectional studies and observational studies in epidemiology, including their strengths and limitations.

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