Speaking of charts and clear communication, here's a reminder that there are some who use charts in a way that can be deceptive. Dennis Donovan, a math teacher at Xaverian Brothers High School in Westwood, MA, points out that a graph on the DirecTV.com home page (scroll to the bottom) offers a good example of an advertisement using a graphic (in this case a column chart) which clearly distorts the data being presented.
The message that DirecTV is trying to convey is that "DirecTV Stomps The Competition" when it comes to the number of high definition television channels offered by their service. Specifically, by their count, DirecTV offers 95 HD channels while Dish Network offers 81 and cable television stations offer only 56. If one were to create a column chart to compare these numbers, it might look something like this:
But the chart on DirecTV's homepage looks more like this:
with the height of the DirecTV column over twice as tall as the other two, which implies, visually at least, that DirecTV has over twice as many HD channels as the competition. And of course, with no scale indicated on the left side of the chart, it's difficult to see that the height of the Dish and cable columns don't match the number of HD channels they represent.
Sneaky? Yes. Uncommon? Unfortunately, no. There are plenty of other examples like this, and not just in advertising, so don't necessarily believe something just because it's in a pretty chart.