Year	Number of
1990	0.84
1991	0.91
1992	0.98
1993	1.05
1994	1.09
1995	1.1
1996	1.13
1997	1.17
1998	1.21
1999	1.25
2000	1.28
2001	1.3
2002	1.33
2003	1.4
2004	1.51
2005	1.59
2006	1.65
2007	1.72
2008	1.78
2009	1.82
2010	1.86
2011	1.9
2012	1.94
2013	1.99
2014	2.03
2015	2.08
2016	2.1