Year	number
2004	7
2005	6.892857142857143
2006	6.964285714285714
2007	6.928571428571429
2008	6.928571428571429
2009	6.964285714285714
2010	7
2011	7
2012	7.0344827586206895
2013	7.266774193548388
2014	7.266774193548388
2015	7.299032258064517
2016	7.299032258064517
2017	7.331290322580646
2018	7.331290322580646
2019	7.331290322580646