Internal and external study validity
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Questions and Answers

What is the primary concern with the Mediterranean diet measurement in this study?

  • Inadequate control group
  • Lack of randomness in sampling
  • Insufficient sample size
  • Measurement error or bias (correct)
  • Why is generalizability of the study's findings potentially limited?

  • Since the study only assessed prostate cancer
  • Because the study only examined men (correct)
  • Due to the large sample size
  • Because participants were not randomly selected
  • What is a potential consequence of confounding in observational studies?

  • It ensures the accuracy of self-reported data
  • It has no impact on the study's internal validity
  • It can create or mask associations between variables (correct)
  • It always leads to underestimation of associations
  • When is it particularly important to consider confounding effects?

    <p>When the results contradict previous evidence</p> Signup and view all the answers

    Why is it crucial to consider biological mechanisms in observational studies?

    <p>To understand the underlying causal relationships</p> Signup and view all the answers

    In a study where the sample is limited to a specific population subgroup, what should be avoided?

    <p>Generalizations to the general population</p> Signup and view all the answers

    What is a potential limitation of a study conducted among male Health Professionals in the US?

    <p>It is not representative of the general population</p> Signup and view all the answers

    When is it more flexible to generalize study results to the general population?

    <p>When studying a biological mechanism</p> Signup and view all the answers

    What determines the generalizability of a study's findings to other similar populations?

    <p>Certain assumptions</p> Signup and view all the answers

    What should be considered when deciding whether to use a study as part of recommendations?

    <p>The study's limitations and assumptions</p> Signup and view all the answers

    What is the primary factor that determines the role of chance in our results?

    <p>The p-value and 95% confidence intervals</p> Signup and view all the answers

    What is the purpose of examining the width of the confidence interval?

    <p>To get an idea of the precision of the estimate</p> Signup and view all the answers

    What is the main concern when assessing the internal validity of a study?

    <p>Whether the results are influenced by chance, bias, and confounding</p> Signup and view all the answers

    What does a statistically significant exposure-outcome association indicate?

    <p>That there is a true association in the population we study</p> Signup and view all the answers

    What is the primary concern when evaluating the external validity of a study?

    <p>Whether the findings are generalizable to the population</p> Signup and view all the answers

    What is the primary purpose of identifying and adjusting for confounders in a study?

    <p>To eliminate the effect of confounding variables</p> Signup and view all the answers

    What is a potential limitation of adjusting for confounders in a study?

    <p>It can lead to residual confounding due to unknown or unreliably measured confounders</p> Signup and view all the answers

    What can affect the internal validity of a study despite adjusting for confounders?

    <p>The presence of residual confounding</p> Signup and view all the answers

    Why is it essential to consider confounders in a study?

    <p>To minimize the effect of confounding variables on the exposure-outcome association</p> Signup and view all the answers

    What can be a consequence of not adjusting for confounders in a study?

    <p>Confounding effects on the exposure-outcome association</p> Signup and view all the answers

    Study Notes

    Study Sample & Validity

    • Large random sample comprising 47,867 men, mitigating selection bias.
    • Mediterranean diet assessed via self-reported food intake questionnaires, which may introduce measurement error in exposure assessment.
    • Prostate cancer outcomes sourced from national registries and hospital records, minimizing measurement error in outcome assessment.

    Internal Validity & Confounding

    • Internal validity compromised by potential information bias in exposure variables.
    • Confounding occurs when a third factor potentially distorts the association between exposure and outcome.
    • Impacts of confounding include:
      • Distortion of exposure-outcome relationships.
      • Creation of false associations.
      • Masking of true associations.
      • Misestimation of association strength (overestimation/underestimation).

    Assessing Confounding Impact

    • Expect some degree of confounding in observational studies due to non-experimental conditions.
    • Consider confounding effects when:
      • Unexpected results arise contrary to prior evidence.
      • Biological sense is lacking.

    Minimizing Confounding Effects

    • Ensure sample representation of specific population subgroups (e.g., >65 years old, male smokers, university students).
    • Avoid generalizing findings to the general population; specific assumptions apply when generalizing to similar populations.

    External Validity Considerations

    • Study conducted among male Health Professionals in the US, not representative of the general population.
    • Findings may generalize to Health Professionals in similar countries, particularly in Western nations.
    • Flexibility in generalizing results increases when investigating biological mechanisms.

    Conclusion on Study Validity

    • Evaluate the following in determining internal validity:
      • Chance (random/sampling error).
      • Bias (systematic error).
      • Confounding (uncontrolled third factors).

    Role of Chance in Findings

    • Random sampling inevitably introduces chance; errors can skew results.
    • Statistical significance assessed through p-values and 95% confidence intervals indicates reliability of findings.
    • Caution warranted if confidence intervals are wide, affecting estimate precision.

    Adjusting for Confounders

    • Identify potential confounders pre-study using literature, clinical expertise, and subject knowledge.
    • Adjust for confounders during data analysis to derive confounder-adjusted estimates.
    • Despite adjustments, residual confounding can persist due to unknown confounders or inaccuracies in assessing known ones.

    Identified Confounding Factors

    • Study adjusted for key confounders including:
      • Age and Body Mass Index (BMI).
      • Physical activity levels.
      • Smoking status and ethnicity.
      • Height, diabetes, family history of prostate cancer, and vitamin supplement use.
    • While major confounders were addressed, some residual confounding may still affect internal validity but is unlikely to be significant due to careful adjustments.

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    Description

    Evaluate the internal validity of a study on the Mediterranean diet and its relation to prostate cancer. The study has a large random sample, but potential measurement errors may affect the results. Identify the limitations of the study and their impact on the findings.

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