Year	Number of
1990	0.67
1991	0.7
1992	0.72
1993	0.75
1994	0.77
1995	0.8
1996	0.84
1997	0.87
1998	0.91
1999	0.95
2000	1
2001	1.07
2002	1.14
2003	1.22
2004	1.31
2005	1.4
2006	1.44
2007	1.48
2008	1.51
2009	1.55
2010	1.59
2011	1.65
2012	1.72
2013	1.78
2014	1.85
2015	1.92
2016	1.99