Year	number
2005	23.526315789473685
2006	22.45
2007	22.45
2008	21.95
2009	21.476190476190474
2010	20.857142857142858
2011	20.15
2012	19.85
2013	19.314285714285717
2014	19.136363636363637
2015	18.428571428571427
2016	17.686363636363637
2017	17.413636363636364
2018	16.95909090909091
2019	16.45909090909091