Year	number
2004	7.1
2005	7
2006	7
2007	7.2727272727272725
2008	7.2727272727272725
2009	6.909090909090909
2010	6.909090909090909
2011	6.909090909090909
2012	6.909090909090909
2013	6.909090909090909
2014	6.818181818181818
2015	6.454545454545454
2016	6.454545454545454
2017	6.454545454545454
2018	6.454545454545454
2019	6.454545454545454