Don’t we know how many people there are? Doesn’t Census or the IRS keep track of everyone? Well, no they don’t, and while we think the government and microsoft and facebook and google know everything about us, they don’t really. They may know more than we might like but every source of data and information has its warts and doesn’t tell the whole story.
So, a company like facebook has a mountain of data about their users – where they’re from, how often they sign on, some demographics (if you provide them in your profile) – but how do they know what their potential universe of users is? They, like everyone else, have to rely on Census population estimates. Even the big financial services, marketing, and advertising firms rely on the Census Bureau for estimates of the population. Somebody has to the be master keeper of our population portrait and the U.S. Census Bureau is the agency to rely on. Yep, they’re the folks that take the Constitutionally required census every 10 years. (Read Clause 3)
Just before the end of the year the Census Bureau released their latest estimates of the total population of states. These figures were the first update of population totals since the release of the 2010 Census results. See the census is taken every ten years so the only way to figure out how the population has changed since the last census is to estimate it. Population changes on by births being added, deaths being subtracted, and somehow capturing how people migrate – within the country and also from foreign countries. That’s the hard part. There is good data on births and deaths because each of those events has to be officially recorded. No one records migration so that becomes the big question mark in figuring out how and where people move – hence, any update from the actual census has to be an estimate because no one really knows for sure.
The Census Bureau prepares estimates of the nation’s population every month but state estimates are done only once a year. Same with estimates for counties and small areas like cities, towns, and villages.
Census does a lot more with estimates producing figures by age, sex, race, and Hispanic Origin. You can see the schedule of release for 2012 here and more detail about how they calculate estimates here.