Year	Number of
1990	1.2
1991	1.25
1992	1.29
1993	1.33
1994	1.37
1995	1.42
1996	1.45
1997	1.49
1998	1.53
1999	1.56
2000	1.6
2001	1.64
2002	1.69
2003	1.73
2004	1.77
2005	1.82
2006	1.85
2007	1.88
2008	1.91
2009	1.94
2010	1.98
2011	2.02
2012	2.06
2013	2.1
2014	2.14
2015	2.18
2016	2.24