Researchers frequently encounter methodological challenges that threaten the validity of their findings. Evaluate the following study design flaws or unexpected clinical trial phenomena and match each specific scenario with the epidemiological concept that best describes the underlying threat to validity.
- An experimental neurostimulation device shows significant subjective improvement when patients are evaluated by the unblinded lead investigator, but shows no benefit when assessed by independent blinded reviewers.Observer bias
- A large database analysis initially links a new antihypertensive medication to an increased risk of pancreatic cancer, but this statistical association completely vanishes after adjusting for concurrent tobacco use.Confounding
- Participants in a dietary intervention trial strictly adhere to the regimen and demonstrate weight loss during the 12-week study period, but their adherence plummets immediately after the study concludes and intensive monitoring ceases.Hawthorne effect
- A retrospective study shows patients undergoing surgical valve replacement have lower 1-year mortality than those receiving medical therapy; however, baseline data reveals the surgical group had significantly fewer medical comorbidities.Confounding by indication
- A new biomarker screening test for pulmonary fibrosis is implemented. Screened patients survive an average of 5 years from diagnosis compared to 3 years for unscreened patients, though the overall disease-specific population mortality rate remains identical.Lead-time bias
Cevap
The correct pairings identify observer bias (unblinded investigator influences outcome), confounding (vanishes after adjustment for smoking), the Hawthorne effect (behavior changes due to being monitored), confounding by indication (baseline health dictates treatment assignment), and lead-time bias (earlier detection increases apparent survival time without mortality benefit).
Each pairing is correct based on foundational biostatistical definitions: observer bias stems from the researcher, the Hawthorne effect stems from the subject, confounding involves a third linked variable, confounding by indication is treatment assignment based on prognosis, and lead-time bias is an artifact of early screening.
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Anahtar Kavram
Internal validity is frequently threatened by specific biases and confounding factors that must be recognized and mitigated through rigorous study design (blinding, randomization, control groups) and statistical adjustment.