Year	Number of
1990	4.71
1991	4.82
1992	4.94
1993	5.04
1994	5.16
1995	5.28
1996	5.31
1997	5.38
1998	5.47
1999	5.58
2000	5.7
2001	5.76
2002	5.85
2003	5.93
2004	6.06
2005	6.2
2006	6.43
2007	6.7
2008	6.99
2009	7.32
2010	7.68
2011	7.95
2012	8.27
2013	8.57
2014	8.91
2015	9.29
2016	9.67