Year	Number
1975	15.38732
1983	9.72676
2002	12.67901
2003	12.0758
2004	12.65282
2005	11.47472
2006	10.4891
2007	10.24769
2008	10.02679
2009	10.33256
2010	9.64018
2011	9.84527
2012	9.58237
2013	9.33028
2014	9.51991
2015	9.93795
2016	10.06635
2017	10.5
2018	10.49757