How Common is Your Birthday? This Visualization Might Surprise You

By Matt Stiles | | Topics: Demographics

It’s baby season in America, with September the busiest month for births on average in the last two decades. So it seemed like the right time to remix this blog’s most-popular post: How Common is Your Birthday?

That old heatmap, which highlighted specific dates for popularity, has been viewed more than 500,000 times here and published across the web. But it was flawed, namely that it used ordinal data (birthday ranks by date) rather than continuous data (actual births counts by date). This graphic finally addresses that problem:

Birthday Heatmap Born Again

By Matt Stiles | | Topics: Demographics

Last year on my birthday I created a quick heatmap visualizing birthdays by their rank on the calendar. Despite its flaws, the graphic went viral by The Daily Viz standards, receiving a quarter million views.

Most of the attention came in the month of May 2012. But what’s been interesting is its long-tail appeal. Every few months or so my traffic spikes — and I always know why. It has been viewed 100,000 times in the last year. This chart from Google Analytics shows the spikes, including one in recent days thanks to links from Radiolab and io9.


Last fall, around the time that birthdays are most common, my wife and I had a baby, Eva, and I’ve found it difficult to keep this blog “daily” while also focusing on my day job. I’m using this most recent traffic spike as inspiration to get blogging again.

I hope, someday soon, to create something that’s more popular than that silly heatmap. Stay tuned.

Follow me on Twitter for updates.

How Common Is Your Birthday? Pt. 2.

By Matt Stiles | | Topics: Demographics

Last weekend’s birthday heatmap post has been hugely popular by The Daily Viz standards, drawing in more than 100,000 readers and tons of social media attention. While I’m excited about the traffic, I’m also worried that the graphic may have misled some readers.

Some people read the map assuming that darker shades represented higher numbers of actual births, even though I tried to explain in the post that the colors were shaded by birthday rank, from 1 to 366, in popularity. Or I thought I did. Because of that, Sept. 16 — the most popular birthday — seems wildly more common than January 1, among the least popular. Both may be relatively close in the raw number of births, even though their ranks are far apart.

Unfortunately, I haven’t yet been able to acquire a list of all dates and total births for each. But last night I compiled a decade’s worth of nationwide birth data by month. Those data show that August, in fact, saw the most births during the 10-year period. Each month is over 3.1 million births, however:

August, of course, has an extra day for potential births, so I created an average births by month field. Viewed that way, September did have more births relative to its size. But notice there isn’t much difference between months in the distribution of the births. Alas, all our birthdays are probably pretty normal:

I should note that this blog is a place for me to experiment with visualization techniques in my own time, and I will occasionally make bad design choices or produce work that is less useful to some. This is one of those times, I suppose. Thanks to Dan DeFelippiWaldo Jaquith and several others who prompted this post. Download the data if you want to create your own visualizations.

Data source: Centers for Disease Control, National Vital Statistics Reports

A Below-Average Birthday

By Matt Stiles | | Topics: Weather

Today’s my birthday, and the weather is great. What’s it been like for past birthdays, I wondered.

The answer: All over the place (sort of like my parents’ moving choices). This quick heat map shows how the weather varied over the years, with the minimum and maximum more than 40 degrees apart. The average is a balmy 80 degrees, a bit warmer than today:

Data sources: Weather Underground, Weatherbase