A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A prospective cohort study is conducted to evaluate the risk of pleural mesothelioma in construction workers exposed to asbestos in Los Angeles. Three hundred construction workers reporting current occupational asbestos exposure were followed alongside 300 construction workers without a history of asbestos exposure. After 8 years of follow-up, no statistically significant difference in the incidence of pleural mesothelioma was observed between the two groups (p = 0.13), even after controlling for known mesothelioma risk factors such as radiation, age, and sex. Which of the following is the most likely explanation for the observed results of this study?
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A
Length-time biasIncorrect. Length-time bias is a screening-study phenomenon where slow-growing tumors are over-detected; it doesn't apply to an incidence study with an 8-year follow-up.
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B
Lead-time biasIncorrect. Lead-time bias is also a screening bias (earlier detection inflates survival) and is unrelated to a prospective cohort design with a too-short follow-up.
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C
Latency periodCorrect. Mesothelioma has a 20-40 year latency, so an 8-year follow-up is too short to detect the disease in exposed workers; the negative result reflects insufficient follow-up.
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D
Berkson biasIncorrect. Berkson bias is a selection bias when both cases and controls are drawn from a hospital population — not relevant to a community occupational cohort design.
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E
Recall biasIncorrect. Recall bias is a differential error in retrospective exposure ascertainment; this prospective cohort design with documented occupational exposures is not subject to recall bias, and mesothelioma's long latency explains the null result.
↑ Tap an answer to reveal the reasoning
Answer: C. Pleural mesothelioma has a notoriously long latency period — typically 20-40 years between asbestos exposure and tumor development. An 8-year follow-up period in workers who are still actively exposed is simply too short to detect the disease, regardless of the strength of the actual association. This is the textbook example of latency period as an explanation for negative findings in an occupational cohort study.
Length-time bias occurs in screening studies when slower-growing tumors are preferentially detected (because they spend more time in a detectable preclinical state), making screening appear to improve survival. Lead-time bias also occurs in screening studies when earlier detection lengthens apparent survival without actually delaying death. Berkson bias is a selection bias arising when cases and controls are both drawn from hospitalized populations, distorting the apparent association.
The teaching point: for diseases with long latency (mesothelioma, many other cancers, chronic lung disease from inhaled toxins), study follow-up must extend well beyond the typical induction period or the result will be falsely negative.
**Why each option:**
**A.** Length-time bias is a screening-study phenomenon where slow-growing tumors are over-detected; it doesn't apply to an incidence study with an 8-year follow-up.
**B.** Lead-time bias is also a screening bias (earlier detection inflates survival) and is unrelated to a prospective cohort design with a too-short follow-up.
**C.** Mesothelioma has a 20-40 year latency, so an 8-year follow-up is too short to detect the disease in exposed workers; the negative result reflects insufficient follow-up.
**D.** Berkson bias is a selection bias when both cases and controls are drawn from a hospital population — not relevant to a community occupational cohort design.