Birthday distribution
Many of my friends have birthdays in the next few weeks. This fact prompted a discussion about the uniformity of birthdays. In Outliers, Gladwell makes the case that birthdays of a group of individuals may appear skewed for subtle reasons; however such results shouldn't hold for the populace.
This question is easy to answer with a bit of Googling. A Dartmouth professor has precisely the required data --- though only for a single year.
http://www.dartmouth.edu/~chance/teaching_aids/data/birthday.txt
I used R to make a quick display of the data.
No, that isn't a data problem. There really are two groups of birthdays.
While looking for the overall date of birth data, I discovered another file from the CDC that explains the effect.
http://www.cdc.gov/nchs/data/statab/t941x16.pdf
The data in that file show many fewer births on weekends compared with weekdays. This effect is precisely what we see in the plot, which R helps us validate.
This analysis was good enough for my own personal edification. There is still a bit of work left to make these claims statistically valid, but that isn't my point here.