Year	Number of
1990	7.57
1991	7.69
1992	7.82
1993	7.99
1994	8.18
1995	8.4
1996	8.66
1997	8.96
1998	9.32
1999	9.7
2000	10.11
2001	10.62
2002	11.14
2003	11.75
2004	12.38
2005	13.05
2006	13.69
2007	14.35
2008	15.04
2009	15.72
2010	16.39
2011	16.84
2012	17.34
2013	17.8
2014	18.34
2015	18.99
2016	19.82