One of the main tools Open Doors uses to track and measure the extent of persecution in the world is the World Watch List (#WWL). Opendoorsusa have been monitoring the worldwide persecution of Christians since the 1970s. Throughout the ‘80s and ‘90s, the WWL methodology gradually evolved. In 2012, Open Doors’ research unit, World Watch Research (WWR), comprehensively revised the methodology of the WWL to provide greater credibility, transparency, objectivity and scientific quality. And in 2013 and 2016, Opendoorsusa further refined the methodology. Each year, the World Watch List is independently audited by the only institution with academics dedicated to studying the religious liberty of Christians – the International Institute of Religious Freedom (IIRF).