Year	Number of
1990	1.91
1991	1.95
1992	1.96
1993	2.01
1994	2.02
1995	2.06
1996	2.08
1997	2.1
1998	2.13
1999	2.19
2000	2.21
2001	2.24
2002	2.28
2003	2.32
2004	2.36
2005	2.38
2006	2.44
2007	2.48
2008	2.51
2009	2.55
2010	2.61
2011	2.63
2012	2.67
2013	2.72
2014	2.77
2015	2.81
2016	2.87