How'd they count 300 million Americans?

Answers to your questions about the news.
Oct. 16 2006 6:46 PM

The 300 Millionth American

How do we find him?

Download the MP3 audio version of this story here, or sign up for The Explainer's free daily podcast on iTunes.

The population of the United States is about to hit 300 million. According to the U.S. Census Bureau, the milestone will be reached Tuesday, at 7:46 a.m. EDT. * How did they know when it would happen?

It's a guess. The bureau collects complete census numbers only once every decade, but it puts out population estimates much more often. To get a crude sense of the population between milestone census years, the demographers look at monthly birth and death rates supplied by the National Center for Health Statistics. These come from registered birth and death certificates, which are thought to represent more than 99 percent of all births and deaths.

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate


Given these data, researchers at the bureau can make estimates about the rate of population growth in the next month, or the next year. Once they've made a guess about the total growth for October, the researchers can divide by 31 to get a daily rate, and then by 24 to get an hourly rate. Since they assume that the distribution of births and deaths is uniform throughout the month, they can keep dividing until they have estimates for fractions of a minute. For this month, they're expecting one birth every seven seconds and one death every 13 seconds. At that rate, we'll hit 300 million just before rush hour on Tuesday morning.

The figure of 300 million also reflects an estimate for the number of foreigners who move into the United States every month, and the number of native-born Americans who leave. The latter number also includes  members of the U.S. military who leave the country for posts overseas.

The military adjustment is easy—the Census Bureau can grab the deployment statistics from the Department of Defense. It's much harder to get a handle on international migration. In the 1990s, this information came from government records on legal immigration. To get stats for migration from Puerto Rico, the bureau checked the logs of flights to and from the island and tried to determine the net influx of passengers. 

These methods weren't too effective. In 2000, the bureau checked the new population total from the census against the guesses it had made throughout the 1990s—the running totals were off by almost 7 million. To correct this discrepancy, demographers started looking at new ways to estimate population. They also worked on ways to collect meaningful population data between big census years. Over the last decade, the bureau has developed an annual "American Community Survey," which now gathers census-type information from a sample of about 250,000 addresses per month.

Got a question about today's news? Ask the Explainer.

Explainer thanks Signe Wetrogan of the U.S. Census Bureau.

Correction, Oct. 17, 2006: Due to an editing error, the original version of this piece said the milestone would be reached at 7:46 a.m. Eastern Standard Time. In fact, it was 7:46 a.m. Eastern Daylight Time. (Return to the corrected sentence.)



The End of Pregnancy

And the inevitable rise of the artificial womb.

Doctor Tests Positive for Ebola in New York City

How a Company You’ve Never Heard of Took Control of the Entire Porn Industry

The Hot New Strategy for Desperate Democrats

Blame China for everything.

The Questions That Michael Brown’s Autopsies Can’t Answer


Kiev Used to Be an Easygoing Place

Now it’s descending into madness.


Don’t Just Sit There

How to be more productive during your commute.

There Has Never Been a Comic Book Character Like John Constantine

Which Came First, the Word Chicken or the Word Egg?

  News & Politics
The Slate Quiz
Oct. 24 2014 12:10 AM Play the Slate News Quiz With Jeopardy! superchampion Ken Jennings.
Oct. 23 2014 5:53 PM Amazon Investors Suddenly Bearish on Losing Money
Oct. 23 2014 5:08 PM Why Is an Obscure 1968 Documentary in the Opening Credits of Transparent?
  Double X
The XX Factor
Oct. 23 2014 11:33 AM Watch Little Princesses Curse for the Feminist Cause
  Slate Plus
Oct. 23 2014 11:28 AM Slate’s Working Podcast: Episode 2 Transcript Read what David Plotz asked Dr. Meri Kolbrener about her workday.
Brow Beat
Oct. 23 2014 6:55 PM A Goodfellas Actor Sued The Simpsons for Stealing His Likeness. Does He Have a Case?
Oct. 23 2014 11:47 PM Don’t Just Sit There How to be more productive during your commute.
  Health & Science
Bad Astronomy
Oct. 24 2014 7:00 AM Gallery: The Partial Solar Eclipse of October 2014
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.