The Political Terror Scale (PTS) project was started by Michael Stohl and several graduate students at Purdue University in the early 1980s, essentially as a way of empirically testing whether U.S. foreign aid was being sent to countries that violated international human rights standards, thereby being in violation of federal law. The five level coding scheme employed by the PTS was taken directly from the 1980 Freedom House Yearbook and it has been used ever since.