Year	Number of
1990	0.65
1991	0.68
1992	0.71
1993	0.75
1994	0.79
1995	0.83
1996	0.86
1997	0.89
1998	0.91
1999	0.98
2000	1.12
2001	1.21
2002	1.33
2003	1.4
2004	1.53
2005	1.66
2006	1.78
2007	1.89
2008	2.04
2009	2.14
2010	2.2
2011	2.29
2012	2.37
2013	2.45
2014	2.53
2015	2.61
2016	2.69