http://www.rug.nl/research/portal/files/41711829/cesifo1_wp6448.pdf
https://yougov.co.uk/news/2017/04/26/voting-intention-conservatives-45-labour-29-25-26-/
https://www.elysee.fr/admin/upload/default/0001/03/0090173c1bc9aaa87f21995ae3b88a55f1fda3d0.pdf