Year	Number of
1990	7.44
1991	7.79
1992	8.11
1993	8.43
1994	8.75
1995	9.09
1996	9.45
1997	9.82
1998	10.22
1999	10.63
2000	11.08
2001	11.62
2002	12.2
2003	12.81
2004	13.46
2005	14.14
2006	14.79
2007	15.46
2008	16.2
2009	16.99
2010	17.83
2011	18.6
2012	19.41
2013	20.26
2014	21.15
2015	22.1
2016	23.14