One day this summer I got an email message from a reporter. We had an exchange over email. I was on vacation. Ten days later a story appeared. Here’s my end of the back-story. Pleasantries and personal details omitted.
I’m a reporter with the News & Observer, and I’m hoping you’ll be able to speak with me for a few minutes today for a story I’m working on. My story is about the latest census data from NC, specifically the male/female ratio throughout age, along with the ways it has changed over time. I have some specific questions about why the ratio flip-flops in middle age, and why it used to — but no longer does — flip-flop again in late middle age/early old age.
I’d be happy to try to help you. I’m not familiar with the pattern you’re seeing, however. Can you send me or refer me to the numbers you have?
I’m … interested in why boys outnumber girls, but then later in life women outnumber men… [info on locating a spreadsheet file with the data, then a list of “driving questions”]:
- Boys outnumber girls – why?
- Women outnumber men – why?
- Why have both trends flattened out in the last few decades?
- What drives variation over time and place?
I looked over the numbers, then wrote back.
This looks quite normal to me. There are about 104 boys born for every 100 girls, naturally. That’s apparently evolution’s answer to the fact that, as the weaker sex, males die more often at all ages. Some of that is from social causes — like violence, war, and drunk driving — but it is also natural biology for humans. So you always have more boys born, and then at some point in the age distribution it crosses over and you have more females living.
So it’s an interesting question what makes that change over time, or vary from place to place. Change over time has to do with mortality. For example, men smoke(d) much more than women, so that’s contributes a few years to the age difference in life expectancy, although that is decreasing now. In North Carolina, I would guess that what is going on has to do with our large military presence, and our immigration flows (though I don’t know which way those skew here).
The general movement of the crossover age from younger ages to older ages reflects declining overall mortality, so everyone lives longer. I don’t know why it would have gone back down from 35 to 25 in the last decade. That’s an interesting question — I wonder if the national data show the same thing? I’m sorry I don’t know off hand.
That was off the top of my head. Hoping to have more time to look into it, I tried to set up a time to call, but she was out of time on the story. 10 days later, on page 1 of the News & Observer, was this:
Women giving birth to more boys than girls is “apparently evolution’s answer to the fact that, as the weaker sex, males die more often at all ages,” said Philip Cohen, a professor of sociology at UNC-Chapel Hill.
From, “This looks quite normal to me,” to “What’s happening to all of North Carolina’s men?” That’s something.
Anyway, it doesn’t justify the headline, but there is an interesting pattern here. North Carolina is not unique, but it’s among the states with fewer men from about age 25 to 60. The differences aren’t great, but there has to be a reason, and it’s worth looking at.
Here is the pattern, with North Carolina, California, and New York calculated from the 2010 Census (which isn’t available for every state yet), and the national average from the 2009 American Community Survey: