The way bubbles are filled in encodes quite a bit of identifying information

What’s the News: Standardized tests aren’t as impersonal as you might think. Much as detectives analyze a note’s handwriting to pinpoint its author, scientists have developed a way to identify test-takers, voters, and so on just from the way they fill in bubbles.

How the Heck:

The researchers (from Princeton’s Center for Information Technology Policy) used a set of 92 surveys of 20 questions each to train and test their computer program.
After setting aside eight questions from each survey, they analyzed the remaining 12 to determine the distinctive characteristics of each individual’s bubbling style. Maybe they tend to fill bubbles with a squiggle, or a series of diagonal strokes that point to the right or left, but whatever their quirks, the program learned to identify individual test takers. Its specifications are quite detailed—it draws on 804 different features concerning color and shape of the mark.
To test its abilities, the team then sicced the program on the eight questions it hadn’t seen during its training. If the bubbles had been filled in with random patterns, it would have given the correct answer only one ...