The World Watch List of Open Doors and its underlying statistics are among the most quoted instruments for measuring the discrimination or persecution of Christians and violations of their religious freedom.
What global surveys and country comparisons on persecution are helpful for
Thomas K. Johnson, Thomas Schirrmacher, Christof Sauer. Global Declarations on Freedom of Religion or Belief and Human Rights. The WEA Global Issues Series. Vol. 18. Culture and Science Publishing: Bonn, 2017. 117 pp. ISBN 978-3-86269-135-7.
Christof Sauer (ed.). Bad Urach Statement. Towards an evangelical theology of suffering, persecution and martyrdom for the global church in mission. The WEA Global Issues Series. Vol. 9. Culture and Science Publishing: Bonn, 2012. 91 pp. ISBN 978-3-86269-062-6.
Religious Freedom Series Vol 2: Sauer/Howell (eds): Suffering, persecution and martyrdom. VKW: Bonn, 2011. 356 pp. ISBN: 978-3-86269-008-4. 28 Euro.