Year	Number of
1990	11.13
1991	11.53
1992	11.95
1993	12.36
1994	12.75
1995	13.12
1996	13.38
1997	13.67
1998	13.92
1999	14.08
2000	14.29
2001	14.52
2002	14.83
2003	15.21
2004	15.68
2005	16.17
2006	16.61
2007	17.08
2008	17.6
2009	18.18
2010	18.79
2011	19.15
2012	19.67
2013	20.22
2014	20.84
2015	21.51
2016	22.18