Year	Number of
1990	1.47
1991	1.52
1992	1.58
1993	1.64
1994	1.7
1995	1.75
1996	1.84
1997	1.9
1998	1.94
1999	1.97
2000	2.03
2001	2.04
2002	2.06
2003	2.07
2004	2.12
2005	2.12
2006	2.15
2007	2.17
2008	2.18
2009	2.23
2010	2.28
2011	2.3
2012	2.36
2013	2.36
2014	2.39
2015	2.42
2016	2.46