Thursday, November 30, 2006

Know Your Data

Back in the old days, when I was just a kid pretending to be a demographer (the fire ant Census was particularly difficult, by the way), the Census Bureau issued its data in an old-fashioned but remarkably useful medium known as paper. This meant page after page of eyesight-challenging numbers. At the time it seemed like a huge amount of data. How naive we were!

But paper, youngsters, is a more limiting medium than cyberspace. The data released by the Census Bureau had to fit into the paper volumes they published and mailed out to eager data miners. These limitations still shape much of what the Census Bureau publishes on the Internet, since users often want to be able to see trends over time, and maintaining the same data sets (and presentation formats) makes it easier to do this.

But some data, such as population statistics, is now available in basically raw form. This means that rather than five-year age groups, you can get monthly population estimates by single year of age. This provides data users with the opportunity to create their own age groups, such as 18-to-49 year olds, but it also means that if you want five-year age groups, you will have to add them up yourself. (Or—shameless plug alert—get them from New Strategist Publications. Motto: “Be Glad We Can Add.”)

As the amount and level of data detail swells, it also becomes a bit trickier to navigate through all the different data sets and sources. You might not know, for example, that a particular data set on the Census website was discontinued years ago and is now obsolete. (Household projections.) Or you might be confused about which set of population estimates to use since they are now available monthly.(Use the July 1 estimates.)

As yet another service to all eight of our loyal readers, we are instituting a new feature: Know Your Data. This series will answer your burning questions (ACS or CPS??) as well as questions you never thought to ask (Who created the original poverty threshold?). Feel free to email questions you would like us to address. And stay tuned for our first fact-filled offering in the series, appearing on this blog just as soon as the boss stops looking over this way.

No comments: