Year	years
2003	2.7736
2004	2.744961240310077
2005	2.7647887323943667
2006	2.733561643835616
2007	2.6813333333333333
2008	2.6735099337748345
2009	2.6677631578947376
2010	2.631578947368421
2011	2.584415584415584
2012	2.576923076923077
2013	2.51556886227545
2014	2.516766467065869
2015	2.5137724550898213
2016	2.500000000000001
2017	2.4958083832335336
2018	2.489880952380954
2019	2.4690476190476205