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Normal Curves: Sexy Science, Serious Statistics
Regina Nuzzo and Kristin Sainani
Recent Episodes
Is America really facing an epidemic of vitamin D deficiency? While this claim is widely believed, the story behind it is packed with twists, turns, and some pesky statistical cockroaches. In this episode, we’ll dive into a study on Hawaiian surfers, expose how shifting goalposts can create an epidemic, tackle dueling medical guidelines, and flex our statistical sleuthing skills. By the end, you might wonder if the real deficiency lies in the data.
Statistical topics
- dichotomization
- normal distribution
- standard deviation
- researcher biases
- conflicts of interest
- statistical sleuthing
Methodologic morals
- “Arbitrary thresholds make for arbitrary diseases.”
- “Statistical errors are like cockroaches: Where there’s one, there’s many.”
Note that all blood vitamin D levels discussed in the podcast are 25-hydroxyvitamin D levels given in units of ng/ml. To convert from ng/ml to nmol/L, use the formula: nmol/L=2.5*ng/ml. For example, a vitamin D level of 30 ng/mL corresponds to 75 nmol/L.
Citations
Dr. Rhonda Patrick: Micronutrients for Health & Longevity. Huberman Lab Podcast. May 1, 2022
Noh CK, Lee MJ, Kim BK, et al. A Case of Nutritional Osteomalacia in Young Adult Male. J Bone Metab. 2013; 20:51-55.
Binkley N, Novotny R, Krueger D, et al. Low vitamin D status despite abundant sun exposure. J Clin Endocrinol Metab. 2007;92:2130-5.
Malabanan A, Veronikis IE, Holick MF. Redefining Vitamin D Insufficiency. Lancet. 1998;351:805-6.
Dawson-Hughes B, Heaney RP, Holick MF, et al. Estimates of optimal vitamin D status. Osteoporos Int. 2005;16:713-6.
Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357:266-81.
Cui A, Xiao P, Ma Y, et al. Prevalence, trend, and predictor analyses of vitamin D deficiency in the US population, 2001-2018. Front Nutr. 2022;9:965376.
Ross AC, Manson JE, Abrams SA, et al. The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know. J Clin Endocrinol Metab. 2011;96:53-8.
Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96:1911-30.
Manson JE, Brannon PM, Rosen CJ, et al. Vitamin D deficiency-is there really a pandemic. N Engl J Med. 2016;375:1817-20.
Conti G, Chirico V, Lacquaniti A, et al. Vitamin D intoxication in two brothers: be careful with dietary supplements. J Pediatr Endocrinol Metab. 2014;27:763-7.
Holick, Michael, et al. The UV Advantage. Ibooks, 2004.
Holick, Michael F. The Vitamin D Solution: A 3-Step Strategy to Cure Our Most Common Health Problems. Penguin Publishing Group, 2011.
Szabo, Liz. Vitamin D, the Sunshine Supplement, Has Shadowy Money Behind It. The New York Times. August 18, 2018.
Lee JM, Smith JR, Philipp BL, Chen TC, Mathieu J, Holick MF. Vitamin D deficiency in a healthy group of mothers and newborn infants. Clin Pediatr. 2007;46:42-4.
Holick MF. Vitamin D deficiency: what a pain it is. Mayo Clin Proc. 2003;78:1457-9.
Passeri G, Pini G, Troiano L, et al. Low Vitamin D Status, High Bone Turnover, and Bone Fractures in Centenarians. J Clin Endocrinol Metab. 2003;88:5109-15.
Armstrong, David. The Child Abuse Contrarian. ProPublica. September 16, 2018.
Irwig MS, Kyinn M, Shefa MC. Financial Conflicts of Interest Among Authors of Endocrine Society Clinical Practice Guidelines. J Clin Endocrinol Metab. 2018;103:4333-38.
Demay MB, Pittas AG, Bikle DD, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024;109:1907-47.
McCartney CR, McDonnell ME, Corrigan MD, et al. Vitamin D Insufficiency and Epistemic Humility: An Endocrine Society Guideline Communication. J Clin Endocrinol Metab. 2024; 109:1948–54.
See our detailed notes here
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
Chapters:
- (00:00) - Introduction
- (02:55) - Sources of Vitamin D
- (05:43) - What is Vitamin D & Why Do We Need It?
- (07:07) - Vitamin D Deficiency & Rickets
- (10:03) - Defining Vitamin D Deficiency – Changing the Goalposts
- ...
Sweaty t-shirt dating parties, sex pheromone dating sites, choosing your dating partner by sniffing them up — wacko fringe fads or evidence-based mating strategies? And what does your armpit stain have to do with your kids’ immune systems, or hormonal contraceptive pills, or divorce rates?
In this episode of Normal Curves, Kristin and Regina reach back into the 1990s and revisit the scientific paper that started it all: The Sweaty T-Shirt Study. They bring a sharp eye and open mind, critically examining the study and following the line of research to today. Along the way, they encounter interesting statistical topics—including correlated observations, within-person study design, and bar-chart blasphemy—with a short, surprising detour into Neanderthal sex.
Statistical topics
- Correlated observations
- Within-person study design
- Bar charts
- Data and methodological transparency
- Cherry-picking
- Meta-analysis
- Multiple testing
- Post-hoc analyses
Methodological morals
“Repeat after me: Bar charts are not for numerical data.”
“Those who ignore dependencies in their data are destined for flawed conclusions.”
References
- Nuzzo, R. Ah, Love at first whiff. Los Angeles Times. May 19, 2008.
- Papamarko, S. Pheromone parties attempt to match singles by scent. Yahoo!life. April 12, 2012.
- Sainani, K. Stone Age Gene Swap. Stanford Magazine. November/December 2011.
- Aldhous, P. Darling, You Smell Wonderfully Different. New Scientist. 6 May 1995.
- Wedekind C, Seebeck T, Bettens F, Paepke AJ. MHC-dependent mate preferences in humans. Proc Biol Sci. 1995; 260(1359):245-249. doi:10.1098/rspb.1995.0087
- Hedrick P, Loeschcke V. MHC and mate selection in humans?. Trends Ecol Evol. 1996;11(1):24. doi:10.1016/0169-5347(96)80237-0
- Wedekind C, Seebeck T. Reply from C. Wedekind and T. Seebeck. Trends Ecol Evol. 1996;11(1):24-25. doi:10.1016/0169-5347(96)81061-5
- Wedekind C, Füri S. Body odour preferences in men and women: do they aim for specific MHC combinations or simply heterozygosity?. Proc Biol Sci. 1997;264(1387):1471-1479. doi:10.1098/rspb.1997.0204
- Havlíček J, Winternitz J, Roberts SC. Major histocompatibility complex-associated odour preferences and human mate choice: near and far horizons. Philos Trans R Soc Lond B Biol Sci. 2020;375(1800):20190260. doi:10.1098/rstb.2019.0260
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
- (00:00) - Introduction
- (02:27) - Pheromone Dating Parties
- (06:57) - Pheromone Dating Sites and Genetic Matching
- (10:47) - The Science of HLA Genes and Mate Selection
- (18:08) - Breaking Down the Original Sweaty T-Shirt Study
- (23:08) - Study Design Flaws and Data Transparency Issues
- (27:31) - Statistical Flaws: Correlated Observations Explained
- (35:22) - Analyzing the Study's Questionable Results
- (38:18) - The Pill's Influence on Scent Preferences
- (41:26) - Overstated Conclusions and Wandering Discussions
- (46:09) - Media Reactions and the Study’s Public Impact
- (52:22) - Other Studies and their results
- (55:01) - Conclusion
Welcome to a lively conversation about science that's like a journal club, but with less jargon, more fun, and a touch of PG-13 flair. In this introduction, Professors Regina Nuzzo and Kristin Sainani share how they met in graduate school, what they’ve been doing since then, how they’ll choose edgy topics and journal articles to dissect, and a bit about what makes them tick. Join them for their fresh, engaging take on scientific studies, data analysis, and statistical sleuthing.
Kristin and Regina’s online courses:
Demystifying Data: A Modern Approach to Statistical Understanding
Clinical Trials: Design, Strategy, and Analysis
Medical Statistics Certificate Program
Program that we teach in:
Epidemiology and Clinical Research Graduate Certificate Program
Find us on:
Kristin - LinkedIn & Twitter/X
Regina - LinkedIn & ReginaNuzzo.com
- (00:00) - Introduction to Normal Curves
- (03:49) - How We Met and Our Lasting Friendship
- (05:24) - Career Paths
- (08:07) - The Art of Evaluating Scientific Studies
- (09:06) - Personal Health Journeys and Biases
- (10:48) - Shameless Course Plugs & Teaching
- (12:37) - Podcast Origins & Conclusion
