Year	Number of
1990	8.17
1991	8.3
1992	8.42
1993	8.4
1994	8.73
1995	8.84
1996	8.69
1997	8.77
1998	8.73
1999	9.12
2000	9.57
2001	10
2002	10.83
2003	11.63
2004	12.54
2005	13.56
2006	14.15
2007	14.71
2008	15.84
2009	16.5
2010	17.28
2011	18.03
2012	18.22
2013	18.77
2014	19.82
2015	20.11
2016	20.42