The literature abstracts described in the sections are not exhaustive, but this will be expanded and updated. The overview is intended for professionals to gain an easier access to the relevant literature.

Good scientific research on violent extremism and terrorism using primary source judicial data, with hypothesis testing, with analysis of data using standardized statistical methods, which may be replicated, is scarce.

Despite advances in methodological rigor, there is the issue of the reliability and validity of the data.

Open-source data are often used (unclassified information from print and electronic media and other publicly available sources), which may lead to prejudice and biased information (Safer-Lichtenstein, LaFree,  & Loughran, 2017).

The European Database of Terrorist offenders (EDT) is based on comprehensive primary source judicial information of convicted terrorist offenders, including social, psychological and psychiatric reports.

This empirical database is the result of a European cross-border collaboration between judicial organizations and scientists within the European Union (Alberda et al, 2021).

Validation research

The EDT a enables research into the reliability and validity of the VERA-2R tool. The Inter-rater reliability is good to excellent (de Bruyn et al, 2021, submitted). Test-retest reliability, Discriminant and divergent validity, content validity and predictive validity of the VERA-2R tool are being studied in EU funded research by the Netherlands institute of Forensic Psychiatry and Psychology. This validation research is necessary, it will lead to a more reliable and predictive tool and a more evidence-based violent extremism risk assessment and management, also because risk instruments are often not or not properly validated (Logan & Lloyd, 2019; Logan & Sellers, 2020).