NFC North Birthdays Show No Advantage For Older Kids


The March 4, 2012 edition of 60 Minutes on CBS featured a story about the rising rate of kindergarten “redshirting”. Here is a synopsis from the CBS News website:

"(CBS News) Kindergarten “redshirting” is on the rise. That’s the practice of parents holding their children back from kindergarten so they can start school at age 6 – older, bigger, and more mature than their 5-year-old peers. Some research shows that redshirting will give these youngsters an edge in school, and maybe even in life. But is it fair? After all, as Morley Safer reports, boys are twice as likely to be held back as girls. Whites more than minorities. And the rich redshirt their kids more than the poor."

One piece of evidence presented in favor of kindergarten redshirting comes from the Canadian hockey system. Scan a list of Canadian junior all-stars’ birth days and a common theme is found; most are born in the early parts of the calendar year. Consider that within the context of the cutoff date for junior hockey in Canada – January 1 – and it’s hard to argue that the older, bigger, stronger kids don’t have an advantage.

What about the NFL? Does the trend continue in football as it seems that it would? With a fall cutoff date typical for enrolling in school, we’d expect to see a bias towards fall birthdays if the notion that the older kids have an advantage on the football field.

I took a look at the Lions’ roster (thank you for including birthdays!) to get a feel for the distribution of birthdays over the year. Charting the number of birthdays in each month produced the following:

You’ll notice that spring birthdays outnumber the fall birthdays in the Lions locker room. That’s counter to what we would expect to see if the age advantage displayed in hockey carried over to the NFL. However, looking at one team’s roster doesn’t necessarily give a picture large enough to draw a conclusion. Small sample sizes are subject to “noise” in the data, kind of like when I had a high school class with two others that shared my birthday. That’s random and unexpected.

To cancel out some of the noise I added in the rosters of the other three teams in the NFC North. Here is the distribution of birthdays in that data set:

Adding more data smooths out some of the differences we saw in the data solely based on the Lions roster but does not show any clear bias towards birthdays that would be make for an older child among his school peers. It is also worth noting that the peaks shown in August are not unexpected since that month has historically been one of the most “popular” birth months.

Older kids may have an advantage in hockey and other areas of life but it does not appear that those advantages translate to the football field.

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