Year	Number of
1990	1.31
1991	1.35
1992	1.4
1993	1.44
1994	1.5
1995	1.55
1996	1.59
1997	1.63
1998	1.68
1999	1.73
2000	1.79
2001	1.79
2002	1.8
2003	1.82
2004	1.84
2005	1.86
2006	1.89
2007	1.91
2008	1.94
2009	1.97
2010	2
2011	2.03
2012	2.06
2013	2.09
2014	2.12
2015	2.15
2016	2.19