Year	Number of
1990	1.49
1991	1.51
1992	1.53
1993	1.55
1994	1.57
1995	1.6
1996	1.62
1997	1.65
1998	1.68
1999	1.73
2000	1.78
2001	1.82
2002	1.87
2003	1.93
2004	1.99
2005	2.05
2006	2.11
2007	2.17
2008	2.21
2009	2.26
2010	2.32
2011	2.38
2012	2.45
2013	2.54
2014	2.62
2015	2.7
2016	2.78