Made out of people

Dubious Statistics

So I try not to bring up politics on this blog. There's lots of other wonderful stuff in the world to talk about, like social networks and visualization and temporality research and statistics and ....

Well, let's talk statistics. To do that, I'll need to talk politics for just a moment. Below the fold, perhaps.

Chris Cox is my local US representative. He proudly sends out an Annual Report that discusses government dealings. It's actually useful: I'd never known that having a President costs $365 million a year¹. And it's kind of nice to see the relative sizes of different chunks of the government.

But on the next page, Cox tries to make sure you get his message. And so, using a trick right out of How to Lie With Statistics, he picks some figures that look like what he wants to say.

Looks pretty good! Economic growth is "current"ly higher than it has been in the last few decades!

Until we read the caption.

"Average annual growth in gross domestic product per decade, and for the 12-month period ended March 31, 2004." Why doesn't the chart show 2000-2002? Did those years just not exist? Indeed, given that this decade is less than half over, why pick a decade resolution?

I've gone ahead and prepared a different chart. Let's go to the data. This chart gives us quarterly change in GDP (in normalized dollars). He's not wrong about his numbers--but that doesn't make the chart accurate.

So I went ahead and took one year sliding averages of the percentage growth². It's a pretty noisy graph, so the moving average smooths things out a little. Here's the new variant:

Hm. Looks pretty variable. Economic growth is now climing, but hit a pretty low point recently. It obviously fluctuates a lot.

The other charts do similar things:

Average annual unemployemnt rate per decade, and on June 30, 2004.
...
Average Federal Funds rate per decade, and on June 20, 2004.
...
Average annual rate of increase in the consumer price index per decade, and for the 12-month period ended May 31, 2004.

The figures are, in other words, pretty clearly cherry-picked. This isn't how I want my CEO reporting to me, and this isn't how I want my congressman reporting to me either.

¹ At those rates--a million dollars a day--we could probably outsource the office for considerable savings.

² It occurs to me that the running average of cumulative percentages probably isn't the right measure: growing by 20%, then growing by 10%, isn't an average 15%, it's an average 14%. But that's not what I did here, because I don't want to fighjt with Excel.

July 27, 2004 02:59 PM | TrackBack | in Data and Documents