Are people's birthdays distributed evenly throughout the year?

Matthew:

Are people's birthdays distributed evenly throughout the year, or are there clumps of birthdays in certain months?

-- Mark Holmes, Del Mar Heights

Birthdaywise, we're a very clumpy country. Mostly we're busy birthin' in August, but July and September aren't far behind. If you count back on your fingers, that means we're busy doing something else around the year-end holidays and the cold months. This is the standard explanation for the summer rush. If you look at the statistics, February is the month with fewest births, but of course we only have a 28-day window of opportunity then, so that's sort of an artifact.

Things are quietest on the perinatal front from November through January, probably because, from February through April, we're falling asleep in front of the TV after all that holiday humping. And these are broad trends; from year to year, variations can occur.

According the Hallmark card folks, we average 700,000 birthdays every day. They also say the market for birthday cards for centenarians has grown tenfold in the last 40 years (108,000 people 100+). And if they're right that every birthday guy or gal gets an average of eight cards and four presents, I want to know who's been getting my share every year