Year	Number of
1990	9.87
1991	10.01
1992	10.14
1993	10.27
1994	10.44
1995	10.63
1996	10.79
1997	11
1998	11.23
1999	11.62
2000	12.03
2001	12.32
2002	12.64
2003	12.95
2004	13.31
2005	13.67
2006	14.15
2007	14.65
2008	15.21
2009	15.82
2010	16.48
2011	16.98
2012	17.51
2013	18.07
2014	18.67
2015	19.34
2016	20.03