A certain category of design gaffes can be boiled down to violations of audience expectations. Websites that don't work in Internet Explorer are a heck of a nasty surprise for users who, bless their souls, want the same Internet experience as everyone else. Websites that prevent copying, whether through careless text-as-image conversions or those wretched copyright pop-ups from the turn of the century, cripple a feature that works nearly everywhere else on the Internet. Avoiding this category of blunders is crucial to good design, which is why I am upset that one particular pitfall has been overlooked with extreme frequency.
Statistical literacy is the ability to read and interpret summary statistics in the everyday media: in graphs, tables, statements, surveys and studies. Statistical literacy is needed by data consumers.
The importance of statistical literacy in the Internet age is clear, but the concept is not exclusive to designers. I'd like to focus on it because designers must consider it in a way that most people do not have to: statistical literacy is more than learning the laws of statistics; it is about representations that the human mind can understand and remember.