Year	Number of
1990	6.57
1991	7.08
1992	7.63
1993	8.2
1994	8.76
1995	9.24
1996	9.61
1997	9.86
1998	10.08
1999	10.08
2000	10.2
2001	10.59
2002	11.24
2003	11.97
2004	12.76
2005	13.4
2006	14.85
2007	16.14
2008	17.66
2009	19.23
2010	20.93
2011	21.68
2012	22.47
2013	22.97
2014	23.61
2015	24.35
2016	24.87