Year	Number of
1990	1.08
1991	1.15
1992	1.23
1993	1.32
1994	1.41
1995	1.51
1996	1.57
1997	1.63
1998	1.7
1999	1.73
2000	1.8
2001	1.84
2002	1.9
2003	1.99
2004	2.11
2005	2.22
2006	2.36
2007	2.45
2008	2.54
2009	2.66
2010	2.8
2011	2.94
2012	3.09
2013	3.28
2014	3.49
2015	3.73
2016	4.01