Saturday, May 07, 2011

Why we (used to) have editors

Dear CNN:

No, it isn't. It's nowhere near that. I hardly know where to start with this one, but you have to start* somewhere, so -- no.

Even if the hed hadn't overstated our household April gasoline cost by a factor of five or more, that's not the "monthly" bill. The point of the story, to the extent that it has one, is that rising prices produced a certain national average for April. The monthly bill for 2011 would be lower, and the monthly bill for academic year 2010-2011 would be lower still. If you have some reason to think April was typical, you sort of ought to tell us. But that points to a different issue, so let's look at the prose itself:

NEW YORK (CNNMoney) -- Round-trip airfare from New York to Los Angeles. More than a dozen dinners for two at Applebee's. Two 16 GB iPod nanos.

These are just a few of the things you could have bought if you weren't spending $368.09 a month on gasoline.

See above: I'm not, and the amount I spent in April 2011 isn't an accurate reflection of my spending "a month" anyway. But there's a larger and stupider assumption in play. I'm happy to stipulate that it's possible to buy a ticket for a round-trip cross-country flight for $368, but I was buying gasoline in March too -- and in February and January and December. So it isn't as if I'm giving away two iPods a month that I wasn't giving away before. The April-to-April difference in dinners for two at Applebee's is less than four.

That's the average amount American households spent on gas in April, according to an exclusive analysis of data by the Oil Price Information Service for CNNMoney.

The study, which compared average gas prices with median incomes nationwide, also showed that U.S. households spent nearly 9% of their total income on gas last month.

This could be an "exclusive" in the sense that the chicken tartare is exclusive -- nobody in their right mind is taking any. Even so, it'd be nice to supply the missing numbers: What assumptions about miles driven and miles per gallon is this based on? Those are central to helping me determine how close "I" am to the fictional "you," but they aren't the only parts. So here are a couple of ideas you can use to help understand what an "average" means, as well as to annoy reporters who present stories like this one as if they were ready for publication: "range" and "variance."

If you're packing for an April at the beach, it doesn't do you much good to know that the average temperature is 70 degrees. You want to know what 70 is the average of, because you'll make different packing decisions if 70 is the average of 68 and 72 than if it's the average of 40 and 100. That's "range." But you also want to know what the curve is shaped like -- how many 40s and 65s and 68s and 72s and 75s and 100s have gone into the average ("variance").** If there's one 40-degree day every third April, just go to the mall and buy a sweatshirt if you happen to hit that particular year. But if there are five 40-degree days each April, pack accordingly.

From the story, average April household spending on gasoline and the proportion of income that represents go from $435 (14+%) in Mississippi to $89 (2%) in DC.*** Looking at those, and speculating about all the other stuff that's slopping around in all the necessary measures,**** one gathers that telling any individual household what "you" are spending month by month seems like a fundamentally dumb idea. Especially if you're running stories like "Oil price collapse pays off for one speculator" on the same day.

Minor aside. I ran across this story as part of Friday's roundup of how-the-socialisms-are-destroying-America news over at the Drudge Report, hedded "Eats 9% of household budgets." That's a reminder that people who compare cable TV news on a right-to-left scale are missing the point. The choice between a network like Fox, which uses numbers misleadingly for partisan purposes, and one like CNN, which uses numbers misleadingly because it doesn't know what it's doing, isn't much of a choice at all. What we're missing is a network whose news department uses numbers at the basic level of competence expected from its sports department.

* Or you could note that "retail" gas is the only kind households buy; the graphic probably means "regular" gas.
** For bonus points, what does "standard deviation" represent?
*** The story isn't clear on whether that means the district itself or, say, somebody commuting from Woodbridge.
**** Median household income isn't an average; it's a measure of central tendency.

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Anonymous raYb said...

I'd like to know what I wasn't buying last month when gasoline cost nearly $4. The increase in the amount spent on driving my Hummer or SMART car around would be a factor in what I'm doing without. Unless I had the foresight to buy all the gadgets and dinners when gasoline was a cheap $3.509 a gallon.

9:40 AM, May 08, 2011  

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