Year	Number of
1990	1.76
1991	1.8
1992	1.85
1993	1.89
1994	1.93
1995	1.96
1996	1.98
1997	2
1998	2.01
1999	2.02
2000	2.03
2001	2.07
2002	2.11
2003	2.17
2004	2.22
2005	2.29
2006	2.33
2007	2.39
2008	2.44
2009	2.5
2010	2.57
2011	2.63
2012	2.69
2013	2.74
2014	2.8
2015	2.86
2016	2.92