https://www.hamiltonproject.org/assets/files/UnionsEA_Web_8.19.pdf
http://www.bsa.natcen.ac.uk/latest-report/british-social-attitudes-34/key-findings/context.aspx?_ga=2.25464057.552181158.1498632950-1412959047.1496247036
https://esg.wharton.upenn.edu/zicklin-center/zicklin-bright-index/
http://visegradinsight.eu/app/uploads/2019/11/EaP-2030-Trends.pdf