Year	Number of
1990	1.34
1991	1.38
1992	1.41
1993	1.43
1994	1.45
1995	1.47
1996	1.54
1997	1.69
1998	1.86
1999	1.95
2000	2.1
2001	2.19
2002	2.27
2003	2.36
2004	2.45
2005	2.45
2006	2.48
2007	2.52
2008	2.6
2009	2.67
2010	2.74
2011	2.77
2012	2.82
2013	2.93
2014	3.03
2015	3.13
2016	3.24