Year	number
2004	6.461538461538462
2005	6.431818181818182
2006	6.409090909090909
2007	6.454545454545454
2008	6.454545454545454
2009	6.409090909090909
2010	6.318181818181818
2011	6.295454545454546
2012	6.288888888888889
2013	6.516530612244898
2014	6.475714285714286
2015	6.3736734693877555
2016	6.3736734693877555
2017	6.3422448979591834
2018	6.2942857142857145
2019	6.307551020408163