Year	Number of
1990	0.4
1991	0.45
1992	0.51
1993	0.57
1994	0.65
1995	0.73
1996	0.81
1997	0.89
1998	0.97
1999	1.07
2000	1.18
2001	1.19
2002	1.2
2003	1.21
2004	1.21
2005	1.22
2006	1.26
2007	1.29
2008	1.32
2009	1.36
2010	1.4
2011	1.43
2012	1.46
2013	1.49
2014	1.52
2015	1.55
2016	1.59