Year	Number of
1990	1.31
1991	1.35
1992	1.39
1993	1.43
1994	1.48
1995	1.53
1996	1.59
1997	1.64
1998	1.71
1999	1.76
2000	1.83
2001	1.88
2002	1.93
2003	1.99
2004	2.04
2005	2.1
2006	2.17
2007	2.23
2008	2.3
2009	2.39
2010	2.47
2011	2.56
2012	2.68
2013	2.82
2014	2.95
2015	3.08
2016	3.22