Year	Number of
1990	3.9
1991	4.09
1992	4.29
1993	4.14
1994	4.14
1995	4.27
1996	4.1
1997	4.2
1998	4.13
1999	4.08
2000	4.2
2001	4.28
2002	4.3
2003	4.38
2004	4.41
2005	4.43
2006	4.7
2007	4.87
2008	5.07
2009	5.22
2010	5.44
2011	5.65
2012	5.97
2013	6.19
2014	6.46
2015	6.79
2016	7.1