Shingles Shot and Dementia: Could one vaccine protect your brain?

What do chickenpox and shingles have to do with your brain? This week, we dig into two 2025 headline-grabbing studies that link the shingles shot to lower dementia rates. We start in Wales, where a birthday cutoff turned into the perfect natural experiment, and end in the U.S. with a multi-million-person megastudy. Featuring bias-variance Goldilockses, Fozzy-the-Bear regression discontinuities, a Barbie-versus-Oppenheimer showdown for propensity scores – and the hottest rebrand of inverse-probability weighting you’ll ever hear.

Statistical topics
• Absolute vs. relative risk
• Bias–variance tradeoff
• Causal inference
• Censoring
• Confounding
• Fuzzy regression discontinuity design
• Healthy-user bias
• Inverse probability of treatment weighting (IPTW)
• Longitudinal study
• Natural experiment
• Negative controls
• Optimal bandwidth
• Propensity scores
• Selection bias
• Subgroup analysis
• Triangular kernel weights

Methodological morals
• “Propensity scores are the lipstick you put on observational pigs.”
• “Natural experiments are a hot flirtation date with causality.”

References
• Eyting M, Xie M, Michalik F, Heß S, Chung S, Geldsetzer P. A natural experiment on the effect of herpes zoster vaccination on dementia. (pmc.ncbi.nlm.nih.gov/articles/PMC12058522) Nature. 2025 May;641(8062):438-446. doi: 10.1038/s41586-025-08800-x. Epub 2025 Apr 2. PMID: 40175543; PMCID: PMC12058522.
• Polisky V, Littmann M, Triastcyn A, et al. Varicella-zoster virus reactivation and the risk of dementia. (pubmed.ncbi.nlm.nih.gov/41053450) Nat Med. Published online October 6, 2025. doi:10.1038/s41591-025-03972-5
• Sainani KL. Propensity scores: uses and limitations. (onlinelibrary.wiley.com/doi/10.1016/j.pmrj.201…) PM&R 2012; 4:693-97.

Detailed Show Notes Page (normalcurves.com/p/detailed-notes-for-shingles…)

Kristin and Regina’s online courses:

Demystifying Data: A Modern Approach to Statistical Understanding (online.stanford.edu/courses/som-xche0033-demys…)
Clinical Trials: Design, Strategy, and Analysis (online.stanford.edu/courses/som-xche0030-clini…)
Medical Statistics Certificate Program (online.stanford.edu/programs/medical-statistic…)
Writing in the Sciences (coursera.org/learn/sciwrite)
Epidemiology and Clinical Research Graduate Certificate Program (online.stanford.edu/programs/epidemiology-and-…)
Programs that we teach in:
Epidemiology and Clinical Research Graduate Certificate Program (online.stanford.edu/programs/epidemiology-and-…)

Find us on:
Kristin - LinkedIn (linkedin.com/in/kristin-sainani-642b5914) &Twitter/X (x.com/KristinSainani)
Regina -LinkedIn (linkedin.com/in/reginanuzzo) &reginanuzzo.com/ReginaNuzzo.com (reginanuzzo.com)

• () - Intro and first gratuitous mention of sex

• () - What are shingles, chickenpox, and the vaccines against them?

• () - Fun facts about the varicella zoster and herpes viruses

• () - A natural experiment in Wales

• () - What is the Goldilocks optimal bandwidth?

• () - Fuzzy regression discontinuity design demystified

• () - Shingles vaccine vs dementia showdown

• () - Absolute risk reduction paradox

• () - Effects for men and women differ

• () - A giant longitudinal study

• () - Propensity scores demystified via Barbie and Oppenheimer

• () - Using propensity scores to make matches

• () - Inverse probability of treatment weighting demystified via more Barbenheimer

• () - Attempts to rename IPTW for TikTok

• () - Longitudinal study results

• () - Smooch ratings and methodological morals: pigs and hot dates

Shingles Shot and Dementia: Could one vaccine protect your brain?

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