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. 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. Nat Med. Published online October 6, 2025. doi:10.1038/s41591-025-03972-5
- Sainani KL. Propensity scores: uses and limitations. PM&R 2012; 3-97.
Kristin and Regina’s online courses:
Demystifying Data: A Modern Approach to Statistical Understanding
Clinical Trials: Design, Strategy, and Analysis
Medical Statistics Certificate Program
Epidemiology and Clinical Research Graduate Certificate Program
Programs that we teach in:
Epidemiology and Clinical Research Graduate Certificate Program
Find us on:
Kristin - LinkedIn & Twitter/X
Regina - LinkedIn & 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
