Year	Number of
1990	9.03
1991	9.48
1992	9.94
1993	10.4
1994	10.9
1995	11.44
1996	11.88
1997	12.36
1998	12.92
1999	13.53
2000	14.19
2001	14.47
2002	14.8
2003	15.17
2004	15.6
2005	16.1
2006	16.51
2007	16.96
2008	17.43
2009	17.98
2010	18.62
2011	19.11
2012	19.66
2013	20.22
2014	20.83
2015	21.52
2016	22.29