Year	Number of
1990	1.12
1991	1.15
1992	1.18
1993	1.21
1994	1.24
1995	1.27
1996	1.33
1997	1.39
1998	1.46
1999	1.52
2000	1.6
2001	1.69
2002	1.79
2003	1.89
2004	2
2005	2.12
2006	2.19
2007	2.26
2008	2.33
2009	2.4
2010	2.48
2011	2.54
2012	2.6
2013	2.67
2014	2.73
2015	2.8
2016	2.87