A "false positive" is a term used to describe the error of thinking that something is what it isn't. When the metal detector in the airport security line goes off and you don't have any metal in your pockets, that's a false positive. On the other hand, a "false negative" is thinking that something isn't what it is. A terrorist who carries a bomb past airport security without being detected is a false negative. In airport security, it's okay to have false positives at the expense of greatly reducing false negatives, because just one false negative could be disastrous.

Sometimes it's better to have more false negatives in order to restrict false positives. Gmail's spam filter does a great job of catching spam, but in my experience, a few spams are able to make it past the filter and into my Inbox each day. The spams that make it through are false negatives. Gmail could make a stronger filter to prevent those false negatives from coming through, but the danger with a stronger filter is that some legitimate emails will be marked as spam and won't show up in your email box. An email system that fails to deliver 100% of legitimate emails is unacceptable, so we have to put up with a few false negatives.

False positives and false negatives are found in nature, too. Camouflage, used by the stick insect to fool predators into thinking there's nothing edible, is a false negative trick. A harmless wasp mimic fly, which has the markings of a wasp to keep predators at bay, is a false positive trick.

Advertisers and shady finance companies use false positives all the time to trick you into paying attention. No doubt you've been fooled by one of those drop cards that look like $100 bills that sleazy businesses place on the sidewalk to trick you into picking it up. You've also received junk mail that looks like it contains a check. Gas pumps now make an "error tone" to get you to look at the screen to see what went wrong, only to discover it's just an ad for a rancid corn dog or a car wash. All of these are designed to make you think they are something that they aren't.

The problem with false positives is that people quickly become acclimated to them. It's the "boy who cried wolf" syndrome -- too many false positives lead to false negatives, with unfortunate results. I wonder how many people have thrown away checks, bills, and other legitimate documents because they assumed they were false positives? It almost happened to me about seven years ago.

I got an email from an online postcard business informing me that I had won $5000, but I thought the email was spam and I threw it away. When a second email arrived a couple of days later and had a personalized headline, I paid more attention and realized that I really had won $5000. It's possible that you have accidentally thrown away an important email because you thought it was just another one of the dozens of daily attempts to swindle you.

The use of false positives to trick people into paying attention is a dangerous and growing practice. In the crowded media environment we live in, where advertisers clamor for morsels of attention, the problem will only get worse. What can we do about it? I have no idea. Please share any ideas if you have them!

Mark Frauenfelder – Editor-in-chief of MAKE magazine and the founder of the popular Boing Boing weblog, Mark was an editor at Wired from 1993-1998 and is the founding editor of Wired Online.