Year	Number of
1990	1.33
1991	1.35
1992	1.39
1993	1.42
1994	1.45
1995	1.48
1996	1.5
1997	1.52
1998	1.54
1999	1.55
2000	1.57
2001	1.61
2002	1.65
2003	1.69
2004	1.74
2005	1.79
2006	1.83
2007	1.86
2008	1.9
2009	1.94
2010	1.98
2011	2.02
2012	2.06
2013	2.1
2014	2.14
2015	2.19
2016	2.24