Year	Number of
1990	8.08
1991	8.62
1992	9.14
1993	9.62
1994	10.14
1995	10.65
1996	10.95
1997	11.19
1998	11.37
1999	11.66
2000	12.15
2001	12.01
2002	12.13
2003	12.4
2004	12.9
2005	13.5
2006	14.06
2007	14.8
2008	15.63
2009	16.51
2010	17.25
2011	18.2
2012	19.02
2013	19.88
2014	20.76
2015	21.63
2016	23.04