Year	Number of
1990	1.25
1991	1.37
1992	1.49
1993	1.6
1994	1.67
1995	1.7
1996	1.76
1997	1.83
1998	1.9
1999	1.95
2000	1.99
2001	2.03
2002	2.07
2003	2.2
2004	2.39
2005	2.51
2006	2.61
2007	2.73
2008	2.81
2009	2.89
2010	2.95
2011	3.01
2012	3.08
2013	3.13
2014	3.19
2015	3.25
2016	3.28