Year	Number of
1990	0.51
1991	0.54
1992	0.56
1993	0.59
1994	0.62
1995	0.65
1996	0.67
1997	0.7
1998	0.72
1999	0.75
2000	0.78
2001	0.82
2002	0.86
2003	0.9
2004	0.95
2005	1
2006	1.03
2007	1.07
2008	1.1
2009	1.14
2010	1.18
2011	1.21
2012	1.25
2013	1.29
2014	1.34
2015	1.38
2016	1.46