December 3, 2025Open Access

Facing Methodological Regression: External Validity Failure in Large-Scale Medical Cohorts and the Case of Spurious Cancer Signals in COVID-19 Vaccine Surveillance

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Observational studies reveal cancer risk linked to COVID-19 vaccination, highlighting selection bias in population cohorts.

Cancer risk appears inflated due to selection bias in vaccinated cohorts, and structural flaw impacts outcomes.
Internal validity achieved, yet misinterpretation of signals due to flawed cohort construction is critical.
Assessment of large-scale medical cohorts across national registries using sophisticated algorithms shows significant biases.
Failure to address external validity risks long-term implications for biostatistics and public health efforts in Europe.

Roccetti, Marco (2025) studied this question.

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