Year	Number of
1990	9.15
1991	9.49
1992	9.87
1993	10.26
1994	10.68
1995	11.11
1996	11.48
1997	11.86
1998	12.27
1999	12.68
2000	13.1
2001	13.53
2002	13.97
2003	14.46
2004	14.97
2005	15.5
2006	15.93
2007	16.37
2008	16.83
2009	17.32
2010	17.86
2011	18.33
2012	18.85
2013	19.37
2014	19.88
2015	20.39
2016	20.96