Year	Number of
1990	10.14
1991	10.71
1992	11.32
1993	11.99
1994	12.72
1995	13.53
1996	13.91
1997	14.34
1998	14.84
1999	15.34
2000	15.81
2001	16.58
2002	17.36
2003	18.18
2004	19.08
2005	20.09
2006	20.3
2007	20.54
2008	20.83
2009	21.13
2010	21.45
2011	21.87
2012	22.32
2013	22.82
2014	23.35
2015	23.91
2016	24.45