Editing 1950: Chicken Pox and Name Statistics

This comic uses Munroe's often-demonstrated love of statistics to point out some non-intuitive correlations.  The first panel sketches out the prevalence of chicken pox by age in the United States. Chicken pox (or varicella) is a highly contagious viral illness that typically causes an outbreak of itchy blisters across the entire body. Most patients recover after a week or so, though some people experience chronic recurrences and serious complications are possible. As the graph indicates, prior to the introduction of the varicella vaccine in the United States, it was an exceptionally common childhood illness, with almost 100% of the population experiencing it at some point. The illness is highly memorable (since the symptoms last for days and are intensely uncomfortable) and noticeable (since the characteristic blisters are distinctive and difficult to hide), meaning that it was once a common experience that people expected to both experience and see in their peers. As the vaccine became widespread in the US, rates of varicella infection declined dramatically, and new infections are now relatively uncommon in the United States. The graph points out that this has led to a fundamental shift in experiences by age. For an American over the age of 30, nearly all your peers growing up would have had chicken pox. For an American under the age of 10, virtually none of them would have had it. This means that older people are likely to think of chicken pox as a normal part of life, while children are likely to have no experience with it, and may not even know what it is.  

The second, seemingly unrelated graph, charts the popularity of certain name over time, in the US. It's normal and expected for certain names to rise and fall in popularity over time, which means that the number of people with those names ends up clustered by age. The names "Sarah" and "Brian" have gone from being highly popular to relatively uncommon for new babies, meaning that people with those names are much likelier to be older. Names like "Logan", "Brooklyn", "Jaxon" and "Harper" went from being virtually unused to having a spurt of popularity, meaning that (as of 2018) people with those names are much more likely to be under the age of 15 than over it.

The final panel points out that these trends, taken together, generate the interested effect that you can, in some cases, estimate the odds of someone having had chicken pox, based solely on their first name. Having a name like "Brian" or "Sarah" raises the odds that you're over 30, which raises the odds that you had chicken pox. People named "Harper" or "Jaxon" are almost certainly young enough to have grown up with the vaccine in broad use.  These time-based trends predict both the odds of a person having had the illness personally, and the odds that they grew up in a time when infections were common and generally expected.  

The cartoon demonstrates a particular type of correlative-based fallacy, i.e. what can go wrong if one attempts to draw conclusions based on a random comparison of two variables. In this case, there's a real correlation between names and the incidence of a particular disease. A superficial reading could suggest that either certain names make people prone to the disease, or that the disease, in some way, impacts a person's name. The real cause of this correlation is simply that certain trends just happen to coincide, causing them to statistically correlate without either variable having a real causal affect on the other.  

The citations are real articles. The first citation ''DOI:10.15585/mmwr.mm6534a4'' is on the Center for Disease Control web site at [https://www.cdc.gov/mmwr/volumes/65/wr/mm6534a4.htm] and the second citation ''DOI:10.1016/j.vaccine.2012.05.050'' is an article in Elsevier at [https://www.sciencedirect.com/science/article/pii/S0264410X12007761?via%3Dihub]. Both articles describe the effects of the vaccine for varicella which is the virus that causes chicken pox and shingles (also known as herpes zoster).

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:[The comic is divided into three vertical frames, and a caption.]

:[Title of the first panel:]

:(Very rough US estimates based on DOI:10.15585/mmwr.mm6534a4 and DOI:10.1016/j.vaccine.2012.05.050)

:[A graph is shown with the y-axis ranging from 0 to 100% and the x-axis labeled "Your age:" ranging from 5 to 35. The percentage is close to 0 for ages below 15 and close to 100 for ages above 30.]

:[Arrow pointing at the graph:]

:Vaccine introduced in 1995

:[Title of the second panel:]

:(Source: ssa.gov)

:[A graph is shown with the x-axis labeled "Your age:" ranging from 5 to 35. The graph lists Harper, Sarah, Jaxon, Brian, Brooklyn and Logan. Sarah and Brian are more popular names for older age groups.]

:[Title of the third panel:]

:(Very rough estimate)

:: Sarah: 50%