"I’m sorry, Dave, you aren’t allowed to cheat on your exam."
Caveon, an independent test security company, uses statistics to detect cheaters:
"…Caveon says its analysis of answer sheets is the most sophisticated to date. In addition to looking for copying, its computers… hunt for illogical patterns, like test-takers who did better on harder questions than easy ones. That can be a sign of advance knowledge of part of a test.
The computers also look for unusually large score gains from a previous test by a student or class. They also count the number of erasures on answer sheets, which in some cases can be evidence that teachers or administrators tampered with a test.
When the anomalies are highly unlikely their random occurrence, for example, is greater than one in one million Caveon flags the tests for further investigation by school administrators."
Cheaters Find an Adversary in Technology, The New York Times>>