Year	Number of
1990	7.31
1991	7.55
1992	7.77
1993	8.03
1994	8.31
1995	8.52
1996	8.82
1997	9.31
1998	9.74
1999	10.28
2000	10.55
2001	11.11
2002	11.7
2003	12.28
2004	12.86
2005	13.46
2006	14.09
2007	14.76
2008	15.27
2009	15.77
2010	16.12
2011	16.42
2012	16.67
2013	16.97
2014	17.32
2015	17.73
2016	17.97