Year	Number of
1990	0.44
1991	0.47
1992	0.52
1993	0.59
1994	0.67
1995	0.78
1996	0.9
1997	1.02
1998	1.12
1999	1.18
2000	1.24
2001	1.28
2002	1.3
2003	1.3
2004	1.28
2005	1.3
2006	1.36
2007	1.38
2008	1.39
2009	1.41
2010	1.45
2011	1.47
2012	1.51
2013	1.55
2014	1.58
2015	1.61
2016	1.63