Year	Number of
1990	8.36
1991	8.81
1992	9.1
1993	9.3
1994	9.48
1995	9.68
1996	9.84
1997	10.13
1998	10.45
1999	10.87
2000	11.39
2001	11.28
2002	11.62
2003	12.29
2004	13.48
2005	17.23
2006	18.01
2007	21.07
2008	24.14
2009	26.19
2010	28.61
2011	31.32
2012	33.71
2013	35.99
2014	37.85
2015	38.78
2016	42.04