Year	Number of
1990	2.48
1991	2.61
1992	2.7
1993	2.76
1994	2.88
1995	3.08
1996	3.09
1997	2.99
1998	2.96
1999	3.04
2000	3.07
2001	3.2
2002	3.33
2003	3.44
2004	3.49
2005	3.62
2006	3.68
2007	3.83
2008	4
2009	4.13
2010	4.35
2011	4.53
2012	4.67
2013	4.96
2014	5.03
2015	5.1
2016	5.37