Year	Number of
1990	1.58
1991	1.63
1992	1.69
1993	1.75
1994	1.81
1995	1.89
1996	1.94
1997	2.01
1998	2.1
1999	2.21
2000	2.34
2001	2.4
2002	2.47
2003	2.54
2004	2.61
2005	2.69
2006	2.68
2007	2.68
2008	2.68
2009	2.69
2010	2.72
2011	2.76
2012	2.82
2013	2.88
2014	2.94
2015	3.01
2016	3.08