Year	Number of
1990	0.61
1991	0.68
1992	0.8
1993	0.95
1994	1.16
1995	1.43
1996	1.72
1997	2
1998	2.23
1999	2.35
2000	2.45
2001	2.54
2002	2.53
2003	2.49
2004	2.39
2005	2.44
2006	2.65
2007	2.8
2008	2.94
2009	3.07
2010	3.2
2011	3.26
2012	3.33
2013	3.4
2014	3.49
2015	3.59
2016	3.69