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.
With this U.S. foreign aid focus, the PTS originally only coded 59 countries. However, in 1984 Mark Gibney began directing the project and he has remained in this capacity ever since. The most noteworthy change is the expansion of the PTS to the entire world, and as new states are created the PTS has grown accordingly. However, what is also remarkable is how the PTS has expanded from its original use involving U.S. foreign aid (Stohl et al.) and refugee protection (Gibney) to now include a dizzying array of political phenomena, as reflected in the Bibliography.