Year	Number of
1990	1.71
1991	1.76
1992	1.81
1993	1.87
1994	1.93
1995	2
1996	2.06
1997	2.14
1998	2.22
1999	2.34
2000	2.46
2001	2.53
2002	2.61
2003	2.68
2004	2.78
2005	2.86
2006	2.83
2007	2.8
2008	2.77
2009	2.77
2010	2.8
2011	2.84
2012	2.91
2013	2.97
2014	3.04
2015	3.1
2016	3.16