Year	Number of
1990	0.94
1991	0.98
1992	1.03
1993	1.08
1994	1.13
1995	1.18
1996	1.23
1997	1.27
1998	1.42
1999	1.35
2000	1.33
2001	1.29
2002	1.38
2003	1.43
2004	1.47
2005	1.5
2006	1.58
2007	1.64
2008	1.66
2009	1.67
2010	1.67
2011	1.81
2012	1.85
2013	1.93
2014	2
2015	2.07
2016	2.12