Year	number
2004	6.84
2005	6.649122807017544
2006	6.672413793103448
2007	6.689655172413793
2008	6.431034482758621
2009	6.327586206896552
2010	6.327586206896552
2011	6.322033898305085
2012	6.3559322033898304
2013	6.373384615384615
2014	6.311846153846154
2015	6.250307692307692
2016	6.265692307692308
2017	6.311846153846154
2018	6.274153846153846
2019	6.304923076923076