Percent changes are useful to help people understand changes in a value over time. Again, figuring this one requires nothing more than third-grade math.

Simply subtract the old value from the new value, then divide by the old value. Multiply the result by 100 and slap a % sign on it. That's your percent change.

Let's say Springfield had 50 murders last year, as did Capital City. So there's no difference in crime between these cities, right? Maybe, maybe not. Let's go back and look at the number of murders in those towns in previous years, so we can determine a percent change.

Five years ago, Capital City had 42 murders while Springfield had just 29.

Subtract the old value from the new one for each city and then divide by the old values. That will show you that, over a five year period, Capital City had a 19 percent increase in murders, while Springfield's increase was more than 72 percent.

That's your lead.

Or is it? There's something else to consider when computing percent change. Take a look at per capita to find out.

On to Per capita