Year	Number of
1990	1.14
1991	1.17
1992	1.21
1993	1.26
1994	1.31
1995	1.36
1996	1.37
1997	1.37
1998	1.35
1999	1.55
2000	1.57
2001	1.63
2002	1.67
2003	1.62
2004	1.6
2005	1.62
2006	1.67
2007	1.72
2008	1.73
2009	1.87
2010	1.96
2011	2
2012	2.05
2013	2.13
2014	2.22
2015	2.29
2016	2.35