Year	Number of
1990	1.2
1991	1.23
1992	1.25
1993	1.27
1994	1.29
1995	1.32
1996	1.35
1997	1.38
1998	1.4
1999	1.47
2000	1.62
2001	1.7
2002	1.81
2003	1.88
2004	2.01
2005	2.12
2006	2.19
2007	2.26
2008	2.34
2009	2.41
2010	2.45
2011	2.54
2012	2.57
2013	2.63
2014	2.68
2015	2.74
2016	2.8