Year	Number of
1990	5.25
1991	5.47
1992	5.68
1993	5.9
1994	6.13
1995	6.37
1996	6.5
1997	6.63
1998	6.77
1999	6.92
2000	7.08
2001	7.47
2002	7.88
2003	8.26
2004	8.69
2005	9.19
2006	9.75
2007	10.37
2008	11.04
2009	11.71
2010	12.4
2011	12.89
2012	13.41
2013	13.93
2014	14.47
2015	15.03
2016	15.65