Year	Number of
1990	7.85
1991	8.17
1992	8.51
1993	8.84
1994	9.19
1995	9.58
1996	9.82
1997	9.85
1998	9.82
1999	9.75
2000	9.72
2001	10.09
2002	10.47
2003	10.89
2004	11.44
2005	11.97
2006	12.48
2007	13.1
2008	13.7
2009	14.39
2010	15.02
2011	16
2012	17.16
2013	18.33
2014	19.84
2015	20.97
2016	22.12