Year	Number of
1990	7.39
1991	7.71
1992	8.14
1993	8.71
1994	9.4
1995	10.15
1996	10.91
1997	11.5
1998	12.06
1999	12.51
2000	12.92
2001	13.07
2002	13.43
2003	13.74
2004	14.08
2005	14.25
2006	14.5
2007	14.71
2008	15.08
2009	15.45
2010	15.89
2011	16.1
2012	16.29
2013	16.55
2014	16.93
2015	17.33
2016	17.86