Year	Number of
1990	3.68
1991	3.9
1992	4.02
1993	4.14
1994	4.26
1995	4.37
1996	4.43
1997	4.45
1998	4.45
1999	4.64
2000	4.74
2001	4.78
2002	4.84
2003	4.9
2004	4.97
2005	5.02
2006	5.02
2007	5.05
2008	5.04
2009	5.08
2010	5.15
2011	5.24
2012	5.3
2013	5.35
2014	5.42
2015	5.5
2016	5.58