Build Your Own Baloney Detector

A tool-kit for avoiding being fooled

Sunday, October 31, 2010

Context-Free Statistics

I’ve been noticing this more of late, although I realize it’s been with us for quite a long time. You’ve seen it, too. A new report or an opinion piece will quote some statistic, whether it be a percent of people who watch the Daily Show who lean left or how many cubic kilometers of ice sheet we’ve lost this year. But what they won’t tell you is some context in which to interpret those statistics.

Take the ice sheets: if I told you that Antarctica loses 100 cubic kilometers of ice annually, what would you make of that number? Large? Small? Cause of worry? Or just an interesting datum? Honestly, by itself it’s impossible to tell. What you need to know is how many cubic kilometers of ice are in Antarctica, for example. Or how much that melt will raise sea levels. Or whatever else context will let you interpret that number appropriately for the story at hand. But by itself, unless you’re an expert in this field or have a particularly good sense of how large ice sheets are (or, at least, how large a cubic kilometer really is), the author might as well have not given you this number at all.

Another example, taken from news of yesterday’s “Rally to Restore Sanity and/or Fear”: some of the media coverage was giving the breakdown of Daily Show fans’ political leanings. It was something like 40% liberal, 38% independent, and 19% conservative. So why is this a problem? Well, it’s more subtle than the last example since we all know what 40% is, but ask yourself: what is the point of these stats? If the only point it to know what Stewart’s audience thinks, politically, they’re fine as they are. But if the author is trying (perhaps surripticiously) to suggest that Stewart and/or his audience is more liberal than normal, we need more information to interpret these statistics. Specifically, how representative is this of the demographic the audience is drawn from. Other studies have shown that the Daily Show audience is younger than normal, so you can’t compare their politics or other habits with the entire adult population and be really fair about it. You need to tell us how this compares with the background population that they more specifically belong to. (Similarly, you never see anyone compare the outcomes of a political survey like this with world-wide leanings because it’s not really helpful to know if an American sub-population is more or less conservative than China or South Africa.)

I suspect that often times, reports fall into this trap unintentionally because they’re not necessarily well-trained in the meaning to numerical data and how to interpret it. But I also suspect (yes, this is me ascribing motivations; take from it what you will) that this is done some of the time to gloss over inconvenient contexts and use numbers of pure shock-and-awe.

posted by John Weiss at 14:05  

Wednesday, October 20, 2010

Conservation of Energy

“No Free Lunch” in physics form. The law of conservation of energy states that in a closed system, energy is never created or destroyed. It can change forms (from chemical potential in gasoline to kinetic in a moving car to heat in our brakes, for example), but it’s always there in the same amount. This is one of the most profound, useful, and often depressing laws in physics.

It’s depressing because it means we can’t get something for nothing. Any energy we use has to come from somewhere and at the expense of something else that would otherwise have that energy. Now, often times this is acceptable. Stealing sunlight from the ground of a desert probably costs little ecologically. Stealing a bit of kinetic energy of water in a hydroelectric plant probably does little harm to the river. But it does come at a price and the price may be higher than we wish.

Conservation of Energy is also a useful principle. It can be used as a shortcut if you know where all of the energy is in a system. (For example, those classic physics problems where the energy is all gravitational potential or kinetic are so much faster to do with Conservation of Energy than the straight up way.) It is widely used by physicists to solve problems that would be a hundred times uglier without it.

And the principle is profound because what it says about the universe. At first blush, there’s no reason why the universe would have had to conserve energy (or anything else). Now, it turns out that if the laws of physics are the same in time (that is, laws like gravitation aren’t changing from what they were a billion years ago) , Conservation of Energy is the natural result. In and of itself this is awfully profound and not just a little bit cool. There’s no a priori reason why this would have been the case, at least not with a casual glance. Time-symmetry isn’t obviously connected to energy until you look under the proverbial hood of the physics engine, be down inside, connected they are.

All that is as may be, but what we most care about here is how you can use the principle of Conservation of Energy as a tool. Here’s how: any time some suggests a source of power for anything humans get up to, ask yourself where the energy comes from. Sometimes it’s well-known and obvious: solar cells use sunlight energy. Gasoline is refined from oil, the by-product of the breakdown of living matter millions of years ago. But what about electric cars? Where do they get their energy? Sure, it’s electricity right before they turn it into kinetic energy and drive off. But where does that energy come from? For a true electric car (not a hybrid), it comes from the same place the electricity in your home does. Depending on where you live, this could be from renewable energy sources, coal, or nuclear. So how “green” are electric cars? It depends a lot on which of those sources supplies the electricity.

How about hydrogen fuel cells? The energy there isn’t electric, at least not when it’s stored. It’s stored as chemical potential energy in the form of hydrogen. Hydrogen loooooves to react with oxygen and make water (a by-product we don’t worry about as much as carbon dioxide). In reacting, it releases energy, which can be harnessed to make electricity (or heat, if you prefer to make that instead). Clean, right? Well, maybe. Where do we get the hydrogen? Remember, hydrogen likes to react with oxygen, that’s what makes it a good fuel. It doesn’t exist here on Earth as hydrogen gas very much. We have to make it from water. Oh, dear, wait: if we start with water and end with water, we’ve put back as much energy into the chemical bonds as we’ve taken out. So where does the energy come from? Answer: not from the hydrogen. We need to put energy into the system to break apart the water. Where does that energy come from? Well, that depends on where you live and who builds the plant. It could be electricity from the grid or solar power, for example. But in any case, the energy has to come from somewhere. (In the end, the hydrogen is basically a form of a battery, storing energy for later use. Then again, in a sense, so is gasoline.)

As our energy consumption drives us to use more and more energy, we worry more about the sources. (This is for all kinds of reasons, ranging from environmental to geopolitical.) Conservation of Energy is a valuable tool to help us citizens navigate the rhetoric (some of it dishonest) about energy policy. While it might be a physicist’s favorite principle, it’s time we shared it with everyone else.

posted by John Weiss at 11:46  

Saturday, October 16, 2010

Free Lunches

“There’s no such thing as a free lunch,” goes an old saying. I’m not sure I can agree that it’s strictly true, but it’s still wise advice. We seldom get something for nothing, but people often let themselves be suckered into thinking that someone, often an anonymous stranger, really is giving them free stuff. It’s true that humans can be and often are altruistic and help each other, but that seldom occurs between strangers or between businesses and people.

The “Free Lunch” flag takes many forms, some of which are kind of subtle, some not so much. For example, there are sites that let you play “free” games on the internet. Now, granted, some of these are amateur games that really are being shared free of charge. Mostly, though, something is driving the business model. Often, it’s advertising for either the games’ creator or a third party. This may be an acceptable price to pay to you, in which case: have at it. But remember that there is a price.

More subtle examples of free lunches abound, however. Consider customer loyalty cards. You get discounts (often) for using them, but is that really something for nothing? Nope. Generally, stores are collecting data on your shopping in exchange for the discounts. Again, it might be worth it (the data is usually used only in aggregate, they don’t care about your purchasing patterns particularly), but it’s a price none-the-less.

In the end, the free-lunch problem doesn’t mean that we should refuse offers that look good. But it does mean that anytime we hear about something that sounds too good to be true, we should think about the details and what the (often hidden) costs might be.

posted by John Weiss at 18:33  

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