Year	number
2004	6.637254901960785
2005	6.553719008264463
2006	6.585365853658536
2007	6.5772357723577235
2008	6.4227642276422765
2009	6.32258064516129
2010	6.296
2011	6.2936507936507935
2012	6.3203125
2013	6.354598540145986
2014	6.3035036496350365
2015	6.250579710144928
2016	6.265072463768116
2017	6.282898550724639
2018	6.248115942028986
2019	6.252826086956522