Year	Number of
1990	0.78
1991	0.81
1992	0.83
1993	0.86
1994	0.88
1995	0.91
1996	0.94
1997	0.97
1998	1.01
1999	1.05
2000	1.1
2001	1.15
2002	1.22
2003	1.29
2004	1.37
2005	1.45
2006	1.51
2007	1.58
2008	1.65
2009	1.72
2010	1.8
2011	1.87
2012	1.95
2013	2.03
2014	2.11
2015	2.2
2016	2.36