Year	Number of
1990	6.84
1991	7
1992	7.19
1993	7.39
1994	7.67
1995	8.01
1996	8.32
1997	8.64
1998	8.89
1999	9.3
2000	9.71
2001	10.11
2002	10.52
2003	10.99
2004	11.43
2005	11.8
2006	12.01
2007	12.12
2008	12.35
2009	12.62
2010	12.91
2011	12.82
2012	14.15
2013	14.1
2014	14.25
2015	14.49
2016	14.75