Year	number
2005	24.941176470588236
2006	24.88235294117647
2007	22.789473684210527
2008	22.42105263157895
2009	22.42105263157895
2010	21.63157894736842
2011	20.3
2012	19.238095238095237
2013	18.714285714285715
2014	18.19047619047619
2015	18.19047619047619
2016	18.238095238095237
2017	18.333333333333332
2018	18.19047619047619
2019	15.952380952380953