Are birthdays of the entire population fairly evenly spread out among the 12 months with say 1/12 of all people being born in March and another 1/12 being born in November? Or say, are three times as many people born in June than are born in April?
Weird. I was about to ask something similar. Mind if I add it to this thread?
So there’s 6 billion of us running around right now.
There has got to be a date on the calendar that a tiny majority of us share as a birthday.
Couldn’t be by much, of course, but there’s gotta be one date out there somewhere that has just an itsy bitsy teeny bit more people eating cake on that day.
And now to answer the question:
This is just a guess. I would say that, in America, at least, you’re probably gonna find more babies being born September-November each year.
Why?
New Year’s Eve boink=September birth.
January is cold. Nothing else to do. More boinking=October birth.
Valentine’s day boink=November birth.
Here is WV_Woman’s Rule Of Thumb ™ to try out on yourself:
Look at your day of birth. When is your mom’s birthday? Dad’s? When is their anniversary?
Chances are you were conceived around one of your parent’s birthdays or their wedding anniversary.
No, of course this doesn’t always hold true so spare me the posts saying that it doesn’t apply to you.
–WV_Woman
(The result of the Thanksgiving turkey, Arsenic & Old Lace and Mom’s birthday)
Great, Grimme. It’s 3am and I’m sitting here trying to figure this thing out.
Ya know how it says that May 22nd is the least common birthday?
I can tellya why.
AUGUST!
It’s hot, sticky and miserable in the States. Who would wanna do it?!
Wow- my son’s birthday is May 22 - least common - and it WAS in August - I remember it well.
Thanks WV_Woman for all your AM efforts that yielded up that great birthday website!
Just like Violet9, my birth date turned out to be approximately nine months after my parents’ anniversary as you surmised.
After I posted the birth month, I got to wondering about the 365 days of the year if they were also evenly distributed or not and you anticipated that. Thanks again…Grimme
One word of warning: I trust that the graph on that page is correct, but it’s got the bottom cut off, so it’s a bit misleading. It looks like early October has over twice the birthrate of May, but it’s closer to being only 20% higher.
six months
La la la la. Nothing to see here. Move along. La la la la.
–Cliffy
9 posts and no welcome? Welcome to the board Grimme! Good first question.
Any non-American dopers have any stats from their country? I’ve got access to big databases at work that include birthdates. I’ll try to run a query tonight and see if Oct. 5th holds up.
…if you’re thinking of shakin’ your groove thang before that August humidity sets in, you heterosexual gents and ladies may want to use prophylaxis. Babies conceived around July and therefore born around April have a higher rate of schizophrenia than babies born at other times of year. This may be related to a seasonal virus that has teratogenic effects at a critical stage in fetal development.
I used a database once that consisted of about half a million birthdays. The most common “month” was about mid-September thru mid-October. The least common “month” was mid-April thru mid-May. The variances were pretty even. About 10% above and below the averages, respectively.
I’d be curious to know how this maps out Down Under, though. . .
So is there any evidence that this seasonal variation is due to variation in frequency of intercourse? It could also be due to other factors, e.g. sperm production efficiency (testicles have to be at a lower temperature than the rest of the body to work properly, right?), or something like the seasonal virus mentioned by Shoshana.
This site: http://www.indianpediatrics.net/march-306-312.htm
has a study of seasonality of childbirth in India and goes into reasons. Most popular month is September. Least is April.
Here’s something on Canada from http://www.cicred.ined.fr/rdr/rdr_a/revues/revue79-80/08-79-80_a.html#08.9
“Seasonality of births has been observed in virtually all historical and contemporary populations. In general, two distinct patterns have been identified in modern populations: (1) the American pattern, characterized by a trough in April-May, and a peak in September, (2) the European pattern with an excess of births during spring and summer, and a secondary peak in September. The authors analyze Census and Vital Statistics data for Canada and the provinces for 1881 and from 1926-1989. The result indicate that the Canadian pattern closely approximates the European model, but only since the early part of this century. Thus a radical change took place between the late 1880s and the early part of this century. The evolution of birth seasonality since 1926 was examined in detail as well as its explanations on sociocultural and environmental of this phenomenon. (CANADA, BIRTH, SEASONAL FLUCTUATIONS, THEORETICAL MODELS)”
WV woman, your argument about people not conceiving in the hot and humid months doesn’t hold true for Australia: the most common quarter of the year for births (I can’t find figures by day or even month) is the September quarter
Births per quarter Australia.
Mar.2001 59,900
Jun.2001 62,300
Sep.2001 62,800
Dec.2001 60,700
(Source ABS Cat. No. 3101.0)
Remember that our summer runs from December to February
Huh. I ran a query against 420,000 employees and customers across the country and here are the top 10:
10/10 1343
08/15 1321
09/18 1320
08/12 1306
08/06 1302
10/02 1302
09/29 1300
07/13 1295
08/02 1295
09/13 1291
And the bottom 10:
04/23 1013
04/28 1005
04/13 992
05/09 991
05/01 991
04/19 981
04/25 974
04/20 965
05/22 964
02/29 270
The shot group for most common birthdates seems to be mid-July to early October. The #1 Oct. 10th date may be misleading as that could be due to lazy data input (1 and 0 are next to each other on the numpad) if the birthdate was not known. Feb. 29th of course is the least common, followed by May 22nd as noted by WV_Woman above. FWIW, Oct. 5th was 81st on the list. The shot group for least common birthdates is very tight: Apr. 13 - May 22. Don’t expect much nookie from mid-July to mid-August. This might be due to the fact that there are high birthrates in those months; I expect that very pregnant women probably aren’t in the mood or have been told to stave off hubby’s advances in the final month by their doctors. 
I think I have access to a database of 16 million customers. I’ll see if I can poke around in there.
Hmm.
I wonder why Australians are popping out their kids in September too, considering it’s really hot over there in December?
Could it be because it doesn’t get REALLY cold over there (snow, etc.) and thus the hot weather just doesn’t bother them as much?
Or maybe the whole New Year’s Eve baby thing is universal (one thing the Australians know how to do is party)?
Thanks for your efforts, Horseflesh
There are bits of Australia where it snows, but not many. And, just because we don’t have cold winters doesn’t mean the heat isn’t a bitch. Depending on where you live, summer down here can be an absolutely godawful energy-sapping time. Middle of December to February where I live, all I want to do is imitate a sloth.
Of course, there’s always air conditioned bedrooms. Or sex in the shower.
Damn straight. 