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Mark Nelson

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Innumeracy, continued

May 21, 2008

People with Asperger Syndrome are sometimes characterized as Little Professors. This Autism Spectrum Disorder is often associated with extreme verbosity, which can manifest itself as an insatiable desire to explain things to people. There is a lively meme which contends that the programming universe is full of undiagnosed or borderline Asperger cases.

Could be.

There are certainly a few things that seem to provoke this type of response in me, and one is innumeracy in the press. This  usually presents itself in a story I read in which the numbers are so out of whack that I can't believe they made it past the bare minimum of a writer and an editor.

Today's example is one in which the press freely accepted a ridiculous numerical conclusion that doesn't even stand up to common sense, much less casual mathematical inspection.

Last week, Network Appliance published a press release touting their participation in setting a goofy new world's record.  The know full well that if the news week is slow, this will get picked up by trade magazines looking to fill pages with their beloved Stories of the Offbeat. The first paragraph more or less tells it all:

Sunnyvale, Calif. - May 14, 2008 -- NetApp (NASDAQ: NTAP) and local system provider TIP provided support recently when residents and visitors to the western Austrian state of Vorarlberg took part in a special exhibition on the future of the region's energy (Energiezukunft Vorarlberg). For three days, participants manned 21 bicycle stations to produce over 12.9 megawatt hours (MWh) of energy- enough to power more than 12,000 average American homes for an entire year. NetApp helped by supporting the technical implementation of monitoring and recording the power generation data as it was produced. The result was a new Guinness World Record for Austria for bicycle-generated power, breaking the previous record, which was held by Italy.

Okay, fine, quirky story, and naturally it was picked up by Eweek, the Wall Street Journal, and all the other usual suspects. This Google search is currently yielding hundreds of hits:

+Vorarlberg +guinness "ride into the future"

Wait a second...

As a programmer or engineer, the first thing you should think upon reading this is "Wait a minute... I can power 12,000 homes for a year with 21 bicycles and 3 days? VCs, here I come!"

Yeah, this is obviously ridiculous, and should have never passed the sniff test. Time to find out what is wrong.

First, those power numbers seem kind of fishy. Let's put them to the test.  If 21 bicycles produced 12.9 MWh in 3 days, that means each station is producing continuous power of 8500 W - that's six blow driers set on max.  According to my handy unit converter, that means each rider is producing over 7300 calories per hour. Since the average human takes an entire day to uses something in the neighborhood of 2000 calories, of which a substantial amount goes to waste heat, this figure seems pretty unlikely from the start.

A quick check of the web finds some good biometrics data on the Wikipedia, which suggest that a peak instantaneous maximum for elite road cyclists is under 2 Kw. A sustained one hour output is likely to be limited to a couple of hundred watts.

So the power output was over-estimated by perhaps a factor of 40. But maybe they actually had 40 elite racing cyclists on each station?. This wasn't a peer-reviewed study, so we don't now the methodology, but let's let it go for now as we move on to the next topic.

Little Pink Houses

Even if the power was overestimated a bit, maybe those same cyclists could actually have powered a few hundred houses for a year. That would still be totally awesome!

First we have to know how much electricy the average US home actually uses in a year. It's a little hard to pin this figure down, but the we can accept the 2001 statistics that have been used to bludgeon Al Gore for his home power bill. Given those, a rough annual budget of 10,000 KWh seems to be in the ballpark. If each home uses 10,000 KWh, and the project produced 12,900,000 Wh of power, simple division gives you the number 1,290.

So was the press release off by a factor of 10? Can we really only power 1290 homes for a year?

As if. There's a units problem here as well - the annual usage is measured in KWh, so we are really talking about powering 1.29 homes for a year. And if we then correct for the factor of 40 in the actual generated power, we get a better statistic: the power generated in this project could keep a single American home going for a paltry 12 days.

So the actual numbers are not quite as impressive. I guess that's what happens when you are off by six orders of magnitude.


I don't claim to have Asperger Syndrome, but as this article shows, I do sometimes like to correct the mistakes of others. This habit annoys people, and of course, that insensitivity is associated with Autism Spectrum Disorders. As an example of the ire this can provoke, I recently took American Express to task for wasting my time with a badly botched survey on my personal blog, and received this stinging rebuke:

I suspect that you view yourself as supremely competent and above something as outrageous as goofing up on testing a system that is customer facing (like those incompetents at AMEX!)

Considering the general smugness of the post (and the whole site really), maybe a link proving that the most self confident tend to be the most incompetent wasnt [sic] the best choice.

Ouch! No, the truth is that I don't consider myself supremely competent. In fact, when I publish a post like this, I beg people to check my math, because I almost never get it right the first time.

However, when faced with such an egregious fiction that has been posted to hundreds of news sites, I feel compelled to write a correction like this. First, to get the facts straight. Second, to encourage people to look for bogosity in other places. For example, maybe if people looked with a cynical eye at CIA reports on arms statistics...  oh, sorry, this isn't that kind of blog.

In any case, yes, some people see this type of post as smug and arrogant, and that's a pity. I'd rather have them see it as a public service, and instead vent their wrath on Network Appliance and the entire journalism profession for inability to do basic math.

But that's just me, the Big Professor.

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