Year	number
2003	10.34
2004	10.160714285714286
2005	10.117647058823529
2006	10.014492753623188
2007	9.81159420289855
2008	9.376811594202898
2009	8.914285714285715
2010	8.7
2011	8.285714285714286
2012	8.26388888888889
2013	8.16
2014	7.92
2015	7.7894736842105265
2016	7.5394736842105265
2017	7.328947368421052
2018	7.184210526315789
2019	6.9605263157894735