Year	Number
1998	18.19036
1999	16.37933
2000	15.94418
2001	16.10786
2002	15.82869
2003	15.09584
2004	14.32526
2005	13.7704
2006	13.27895
2007	12.72766
2008	12.05187
2009	11.14771
2010	10.58341
2012	8.93168
2013	8.28001
2014	8.05782
2015	8.1646
2017	7.7759