Critical Assessment of Observational Studies
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Questions and Answers

What does the STROBE statement help evaluate?

  • Qualitative studies
  • Meta-analysis studies
  • Observational studies (correct)
  • Experimental studies
  • External validity refers to whether the results can be generalized beyond the study sample.

    True (A)

    What are the two main components that a checklist for critical assessment of observational studies should have?

    Research question and study design

    A prospective ______ design was used to study the effect of estrogen-progestin combination use on cardiovascular disease.

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

    Which of the following is NOT a key element when considering a study's research question?

    <p>The research question should be included in the conclusion section. (C)</p> Signup and view all the answers

    Match the components of a critical assessment checklist with their descriptions:

    <p>Research Question = Clarity of hypothesis and background Study Design = Type of study conducted Study Population = Characteristics of the participants Data Analysis = Statistical methods and confounding Policy Implications = Relevance to real world practice</p> Signup and view all the answers

    The rationale for investigating the research question should always be found in the study's results section.

    <p>False (B)</p> Signup and view all the answers

    According to Grodstein F, Stampfer MJ, Manson JE, what medical condition were they studying?

    <p>cardiovascular disease or CVD</p> Signup and view all the answers

    What is a key reason observational studies are important in medical literature?

    <p>They allow the examination of rare events and long-term developments. (D)</p> Signup and view all the answers

    The results of observational studies should always be accepted without critical evaluation.

    <p>False (B)</p> Signup and view all the answers

    What type of error occurs when there are systematic differences in how exposures and outcomes are measured between study groups?

    <p>Measurement bias</p> Signup and view all the answers

    A ______ is a factor associated with both the outcome and the treatment but is not a consequence of the treatment.

    <p>confounding factor</p> Signup and view all the answers

    Which of the following best describes selection bias?

    <p>Errors in the estimate of effect due to procedures used to select subjects or other factors that influence the study. (B)</p> Signup and view all the answers

    What is one way to address unobservable confounding factors in observational studies?

    <p>Instrumental variable methods (C)</p> Signup and view all the answers

    Internal validity refers to whether the study results are generalizable to other populations.

    <p>False (B)</p> Signup and view all the answers

    What are two approaches to control for observable confounding factors?

    <p>Stratification and statistical adjustment</p> Signup and view all the answers

    The variable quality of observational studies can compromise their internal and ______ validity.

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

    Match the following terms with their descriptions:

    <p>Selection Bias = Systematic error in how subjects are chosen for a study. Measurement Bias = Systematic error on how exposures or outcomes are measured Confounding Factor = A variable associated with both the treatment and the outcome but is not a consequence of the treatment. Internal Validity = Whether the study results are valid</p> Signup and view all the answers

    What effect does progestin use have on cholesterol levels in relation to cardiovascular disease (CVD)?

    <p>Increases LDL cholesterol and lowers HDL cholesterol (A)</p> Signup and view all the answers

    There is sufficient information on the effects of estrogen-progestin combination use on cardiovascular disease.

    <p>False (B)</p> Signup and view all the answers

    What was the goal of the prospective cohort study design regarding hormone replacement therapy (HRT) and CVD?

    <p>To infer causal relationship between hormone replacement therapy and cardiovascular disease.</p> Signup and view all the answers

    The study selected participants from a source population of ______, with a total sample size of ______ patients.

    Signup and view all the answers

    What is a primary reason for evaluating inclusion/exclusion criteria in study populations?

    <p>To reduce the chance of confounding (A)</p> Signup and view all the answers

    Comparison groups in studies should represent the same group of individuals as treatment groups.

    <p>False (B)</p> Signup and view all the answers

    What should be reported to help assess the comparability of groups in a study?

    <p>Baseline characteristics</p> Signup and view all the answers

    The cohort selected for the Nurses’ Health Study primarily consisted of nurses aged ___ to ___ years.

    <p>30, 55</p> Signup and view all the answers

    Why might the results of the Nurses’ Health Study not be generalizable to the broader population?

    <p>Nurses may be more adherent to medications (B)</p> Signup and view all the answers

    Attrition rates in a study do not need to be reported if they are unrelated to the outcome.

    <p>False (B)</p> Signup and view all the answers

    What analysis method should always be utilized regarding the subjects in a study?

    <p>Intention-to-treat analysis</p> Signup and view all the answers

    Match the following types of studies with their characteristics:

    <p>Case-control study = Has controls that did not experience the outcome Cohort study = Includes a comparison group representing common changes over time Intent-to-treat analysis = Analyzes subjects in their originally assigned groups Attrition = Rates that should include reasons related to the outcome</p> Signup and view all the answers

    What happens to cardiovascular disease (CVD) risk during the first year of hormone replacement therapy (HRT) use?

    <p>It increases during the first year. (A)</p> Signup and view all the answers

    CVD risk is excluded for those who developed it after being initiated on HRT between surveys.

    <p>True (A)</p> Signup and view all the answers

    What methods are commonly used to measure exposure in studies?

    <p>Patient reports, medical records, and pharmacy claims data.</p> Signup and view all the answers

    In case-control studies, a _____ look-back period may underestimate exposure for conditions that develop slowly.

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

    Match the types of hormone replacement therapy (HRT) exposure to their definitions:

    <p>Current estrogen-progestin combination use = Use of a combination of estrogen and progestin at present Current estrogen alone use = Use of estrogen without progestin at present Past use = Any previous use of hormone therapy before the current time Never use = No history of hormone therapy at any time</p> Signup and view all the answers

    Which factor is crucial when determining the look-back period in case-control studies?

    <p>How long it takes the event to develop (B)</p> Signup and view all the answers

    Statistical analysis should not be appropriately adjusted for observed confounding factors in studies.

    <p>False (B)</p> Signup and view all the answers

    What stratifications were made for the current dose of estrogen to examine CVD risk?

    <p>0.3mg, 0.625mg, 1.25mg, and ≥1.25mg.</p> Signup and view all the answers

    Progestin use has been shown to have a beneficial effect on arterial dilation and blood flow.

    <p>False (B)</p> Signup and view all the answers

    Which of the following is NOT a general observational study design?

    <p>Experimental Study (A)</p> Signup and view all the answers

    A ______ cohort study design was used to investigate the relationship between hormone replacement therapy (HRT) and CVD.

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

    What was the primary goal of the prospective cohort study mentioned in the text?

    <p>To infer a causal relationship between hormone replacement therapy (HRT) and CVD.</p> Signup and view all the answers

    Match the following observational study designs with their characteristics:

    <p>Cohort Study = Follows groups with different exposures over time to see who develops the outcome Case-Control Study = Compares people with a disease to people without the disease to identify risk factors Cross-sectional Study = Looks at a snapshot of a population at a single point in time to identify associations</p> Signup and view all the answers

    What is a potential benefit of using a prospective cohort study design, especially when studying rare outcomes?

    <p>Better at establishing causality (B)</p> Signup and view all the answers

    The study on HRT and CVD had a limited number of patients and a short follow-up period.

    <p>False (B)</p> Signup and view all the answers

    What is a key consideration when evaluating the appropriateness of the source population for a study?

    <p>How well it represents the target population for the research question.</p> Signup and view all the answers

    What percentage reduction in risk for major coronary artery disease is indicated by the age-adjusted RR of 0.45 in postmenopausal women using estrogen?

    <p>55% (A)</p> Signup and view all the answers

    The unadjusted rates of major coronary artery disease for the study group were higher than those for the control group.

    <p>True (A)</p> Signup and view all the answers

    What is the number needed to treat (NNT) according to the provided calculations?

    <p>1,183</p> Signup and view all the answers

    Caution should be taken with the use of HRT for primary prevention of ________.

    <p>heart disease</p> Signup and view all the answers

    Match the following terms with their corresponding descriptions:

    <p>Nominal Risk Reduction = Difference of absolute risks Relative Risk = Risk in treatment group vs. risk in control group Absolute Risk = Actual risk reduction observed Number Needed to Treat (NNT) = Number of patients needed to treat to prevent one event</p> Signup and view all the answers

    What is a significant reason for the black-box warnings issued by the FDA?

    <p>Utilizing findings from observational studies (B)</p> Signup and view all the answers

    It is recommended that practice implications should be based solely on one study’s findings.

    <p>False (B)</p> Signup and view all the answers

    What did the authors conclude about the addition of progestin to estrogen regarding cardioprotective effects?

    <p>It does not appear to attenuate the cardioprotective effects.</p> Signup and view all the answers

    Flashcards

    STROBE Statement

    A set of guidelines that helps evaluate the quality of observational studies in epidemiology.

    External Validity

    The extent to which the results of a study can be generalized to other populations and settings.

    Research Question

    A well-defined question that guides the research, including any specific predictions.

    Study Design

    The method used to collect data, such as cohort studies, case-control studies, or cross-sectional studies.

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    Study Population

    The group of individuals who are included in the study.

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    Exposure

    The variable or factor being investigated, such as exposure to a drug or a specific lifestyle factor.

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    Outcome

    The health outcome being measured, such as disease development or disease progression.

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    Data Analysis and Confounding

    The process of analyzing data to identify associations between exposure and outcome while controlling for other factors that could influence the results.

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    Bias in observational studies

    Systematic errors in the way subjects are selected, measured, or analyzed, leading to inaccurate study results.

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    Selection bias

    A type of bias that occurs when subjects selected for the study are not representative of the population of interest.

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    Measurement bias

    Bias that happens during data collection, where there are systematic differences in how exposures and outcomes are measured or reported between study groups.

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    Confounding factor

    A factor that is associated with both the outcome and the treatment being studied, but is not a consequence of the treatment.

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    Stratification

    A technique used to control for observable confounding factors by dividing the study population into subgroups based on the confounding variable.

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    Statistical adjustment

    A statistical method used to control confounding factors by adjusting for their effect on the outcome.

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    Instrumental variable methods

    Methods used to address unobservable confounding factors by using a variable that is related to the treatment but not to the outcome.

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    Heckman selection model

    A statistical model used to address unobservable confounding factors by taking into account the selection process of the study participants.

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    Cohort Study

    A research design that observes participants over a period of time to investigate the relationship between an exposure and an outcome of interest.

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    Case-Control Study

    A research design that compares cases with a specific outcome to controls without that outcome, looking for differences in exposures in the past.

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    Source Population

    In epidemiology, the group of individuals from which a sample is drawn for a study.

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    Target Population

    The group of individuals to whom the results of a study are intended to be generalized.

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    Inclusion Criteria

    Criteria used to determine who is eligible to participate in a study.

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    Exclusion Criteria

    Criteria used to exclude individuals from participating in a study.

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    Cross-Sectional Study

    Observational study design used to investigate the association between exposure and outcome in a population at a single point in time.

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    Case-Series Study or Case Report

    Observational study design involving detailed descriptions of a single case or a small group of cases with a specific outcome or condition.

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    Subject Selection

    The process of selecting participants for a study. This involves understanding the source of the population and applying inclusion and exclusion criteria.

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    Comparison Group

    A group of individuals who did not experience the outcome being investigated. This helps compare the treatment group to a similar group without the intervention.

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    Baseline Characteristics

    Characteristics of study participants that are similar between treatment and control groups. This helps ensure a fair comparison and minimize the influence of other factors.

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    Attrition Rates

    When participants drop out of a study before completion. It's important to understand why attrition happens as it can affect study results.

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    Intention-to-Treat Analysis

    Analyzing all subjects as originally assigned, even if they dropped out of the study. This helps ensure that the results are not biased by attrition.

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    Generalizability

    How well the study findings can be generalized to other populations beyond those included in the study. This depends on the representativeness of the sample to the broader population.

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    Confounding Variables

    Factors other than the intervention being studied that can influence the outcome. It is important to minimize confounding variables to ensure the results are accurate.

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    Inclusion/Exclusion Criteria

    Strict criteria used to select participants for a study. They help reduce confounding variables, but may limit the generalizability of results.

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    Exposure and Outcome

    Exposure is how the researchers measure what they are studying (e.g. hormone therapy use) and outcome is how they measure the result (e.g. cardiovascular disease).

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    How is Exposure Measured?

    Using medical records to accurately measure hormone therapy use is an example of how exposure is measured.

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    How is Outcome Measured?

    Collecting data on heart attacks or strokes is an example of how outcomes are measured.

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    Follow-up Period in Cohort Studies

    In a study looking at long-term effects, ensuring follow-up is long enough to observe the outcome is crucial.

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    Look-back Period in Case-Control Studies

    When studying past exposure, researchers need to look back far enough in time to capture the relevant exposure.

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    Objective Outcome Measures

    Objectively measured outcomes like lab tests or medical records are preferable to subjective reports.

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    Appropriate Outcome Measures

    The outcome measure must be relevant to the study's purpose and provide sufficient details.

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    Adjusting for Confounding Variables

    Adjusting for confounding variables during analysis reduces bias, making the results more reliable.

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    Absolute risk reduction

    The impact of a treatment or intervention on the overall risk of a disease, taking into account the baseline risk in the population.

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    Relative risk ratio (RRR)

    A measure of the strength of association between an exposure and an outcome, expressed as the ratio of the risk of the outcome in the exposed group to the risk in the unexposed group.

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    Number needed to treat (NNT)

    The number of patients who need to be treated with a particular intervention to prevent one adverse event or achieve one beneficial outcome.

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    Observational study

    A study design in which researchers observe and collect data on a group of individuals over a period of time without attempting to manipulate the outcome.

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    Black box warning

    Warnings issued by the FDA based on potential risks associated with a drug or medical device, often derived from observational studies.

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    Randomized controlled trial (RCT)

    Studies designed to compare the effects of different interventions or treatments on a clearly defined outcome.

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    Study Notes

    Evaluating Observational Studies

    • Observational studies are crucial in medical literature, examining rare events and those taking time to develop. They play a role in comparative effectiveness research, offering a realistic view of daily practice.
    • These studies, however, require a critical review due to their inherent variable quality which may threaten internal and external validity. A deep understanding of the study design, its limitations and critical evaluation of the findings are needed. Results should not be automatically accepted; evaluation methods are key.

    Objectives

    • The extent of bias in observational studies should be explained.
    • The necessity for critical appraisal of observational studies needs to be defined.
    • Formal criteria for assessing observational studies should be listed.
    • Design, methods, and analytical approaches in these studies should be evaluated.
    • Results of observational studies should be evaluated alongside randomized controlled trials (RCTs).

    Introduction

    • Bias and confounding are systemic errors found in the selection, measurement, and analysis of observational study subjects.
    • Selection bias is particularly problematic, especially due to lack of randomized treatment assignment. Factors influencing participant in and follow-up of a study can skew results if the selected group is not representative
    • Measurement bias (information bias) occurs during data collection. If there are systematic differences between groups in the way exposures or outcomes are measured or reported by participants, caregivers or researchers, it skews results.

    Bias and Confounding

    • A confounding factor is associated with both the outcome and the treatment, but is not a consequence of the treatment. The factor is not directly related to the treatment.
    • Selection bias can happen if confounding factors aren't balanced between treatment and comparison groups.
    • Controlling for confounding factors includes observable confounding factors, stratification, statistical adjustment, instrumental variable methods, and Heckman selection models.

    General Criteria for Evaluating Observational Studies

    • Internal validity assesses the validity of the study's results, while external validity determines how generalizable the results are to local practice.
    • STROBE (Strengthening the Reporting of Observational studies in Epidemiology) provides a statement to help researchers evaluate observational studies, as well as equip readers with critical appraisal skills for evidence.
    • A checklist for critical assessment includes research question, study design, study population, exposure, outcome, data analysis and confounding, presentation of results, and interpretation of results alongside practice and policy implications

    Research Question

    • Research questions, including any pre-specified hypotheses, should be clearly stated in the introduction.
    • A clear, plausible research question along with its scientific background and rationale is crucial to evaluating observational studies.
    • The study should clearly outline the population being studied and the key outcomes of the research

    Study Design

    • Observational study designs include cohort, case-control, cross-sectional, and case-series (or case reports). These generally need to be applied when the issue is related to the target or source population.
    • The choice of design should be appropriate to address the research questions.

    Subject Selection

    • Determining how subjects were selected is crucial for understanding the generalizability of the results.
    • A thorough description of the source population, along with a comparison to the target population relevant to the research question, is necessary.
    • Adequate documentation of inclusion and exclusion criteria, and characteristics of the study population are needed. A comparison of those characteristics to patients encountered in clinical practice should be addressed.
    • An appropriate comparison group, with a stated justification, is important. The comparison group should be comparable to the treatment group.
    • Careful attention should be paid to the response rate as well as any attrition rate over time and the underlying reasons. Appropriate strategies should address or mitigate potential biases and distortions. Intention-to-treat analysis should be used when appropriate.

    Exposure and Outcome Measures

    • Exposures and outcomes are measured using various reliable methods, such as patient reports, medical records, or pharmacy data. Look-back periods need to be appropriate for case-control studies where assessing long-term outcomes might have delays.
    • Clear and complete documentation explaining the processes used to measure exposes and outcomes is crucial. Outcomes should also be measured objectively appropriate to the specific study.

    Data Analysis and Confounding

    • Statistical tests need to be appropriate for both the design and the measurement of outcome variables. Accounting for rare events and sample size needs to be considered to avoid erroneous conclusions.
    • Multivariable regression analysis should be used to adjust for multiple confounding factors - in regards to both continuous and binary data.
    • Residual confounding may also be an issue and should be assessed, as it could result from unobservable variables.

    Presentation of Results and Interpretation

    • The interpretation and conclusion must be supported by the actual study findings.
    • Risk ratios, odds ratios, and hazard ratios are commonly used.
    • The number needed to treat (NNT) and number needed to harm (NNH) can be reported to help visualize the magnitudes of treatment effects more easily.
    • The choice of measure should be documented and justified.

    Application to Practice and Policy

    • The impact of the findings on clinical practice and public policy should be evaluated.
    • Decisions for practice or policies should not be based on one study alone. Well-designed observational studies can complement findings of RCTs, which are more scientifically rigorous as many FDA black-box warnings were largely based on observational studies, not RCTs.
    • Evaluations should include considering the availability of RCT data during a study, the differences in populations, and the reliability of exposures and outcomes.

    Comparison of Results From Observational Studies and Randomized Trials

    • Results from observational studies and RCTs may sometimes differ. This could be due to methodological variations such as differences between study populations, how exposures are measured, and how outcomes are measured.
    • Different ways for exposures, outcomes and data collection will influence the outcomes findings. Possible explanations for discordant results should be considered, and the implications for practice should then be assessed.

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    Description

    This quiz focuses on understanding the critical components necessary for assessing observational studies, including the STROBE statement and external validity. Test your knowledge of designing checklists for evaluation and learn key elements that are essential to research questions. Ideal for students in epidemiology and clinical research.

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