Year	Number of
1990	2.7
1991	2.79
1992	2.88
1993	2.97
1994	3.06
1995	3.15
1996	3.23
1997	3.3
1998	3.37
1999	3.45
2000	3.53
2001	3.64
2002	3.79
2003	3.93
2004	4.08
2005	4.24
2006	4.4
2007	4.56
2008	4.71
2009	4.89
2010	5.08
2011	5.24
2012	5.42
2013	5.61
2014	5.82
2015	6.02
2016	6.17