How Numbers Lie

Because many of us find statistics both convincing and confusing, lots of tricksters find statistics useful--from politicians, to talking heads, to Madison Avenue's marketers. Here are just three statistical tricks number-liars often employ.

1. Pick Your End Carefully
In this statistical sin, the perpetrator chooses to start or end a comparison at an abnormal point in an ongoing cycle. For example, the temperature outside KnowledgeNews HQ this fall afternoon is 70 degrees Fahrenheit (21 degrees Celsius). But a week ago, the low temperature, in the wee hours of the morning, was 35 degrees Fahrenheit (2 degrees Celsius). Amazing! A 35-degree increase in just one week!

But now, measuring from the low on a cool night to the high on a pleasant afternoon is very misleading, isn't it? In fact, fall temperatures here can range all the way from 90 degrees Fahrenheit in the afternoon to 25 degrees Fahrenheit at night. So the temperature fluctuations over the past week have actually been pretty normal, and not amazing at all.

Where you'll see this trick: When politicians in the U.S. presidential election talk about job gains and losses. Challengers might be tempted to talk about job losses since a high point in the economic cycle, while incumbants might prefer to talk about job gains since a low point.

2. Ignore Normal Growth
Every year, lots of numbers grow on their own, from the population of the United States to the price of the goods and services we buy. And reporters, politicians, and marketers trying to make their points may ignore this normal growth when they report new numbers.

For example, let's pretend the number of Americans who keep pet elephants in their garage has doubled since 1950. Are we about to be overrun by garage-dwelling pachyderms!?! Nope. The total U.S. population has doubled in the same period, from roughly 150 million to over 300 million. So, in this example, the pet elephants are just holding their own.

Where you'll see this trick: When politicians talk about tax increases and tax cuts. They'll lavish praise on "the biggest tax cut in history," ignorning population growth and inflation, and heep scorn on "the biggest tax increase in history," again ignorning population growth and inflation.

3. Treat Exceptions as Rules
People find concrete cases more persuasive than abstract statistics. Marketers and politicians know this, and they respond by using "best case" examples that often grossly misrepresent their product or policy. Think of ads for diet supplements, complete with "before" and "after" pictures and "results not typical" disclaimers buried in the fine print.

Such ads want you to think that you will, in fact, achieve the same results. Of course, statistically speaking, you probably won't. That's what "results not typical" means.

Where you'll see this trick: Typically, during speeches at political conventions. Both presidential candidates like to single out typical-seeming families who would benefit greatly from the candidates' programs. Maybe those families should have to wear t-shirts that say "results not typical."

--Steve Sampson