Year	Number of
1990	6.36
1991	6.58
1992	6.85
1993	7.13
1994	7.44
1995	7.78
1996	8.09
1997	8.44
1998	8.78
1999	9.12
2000	9.48
2001	9.78
2002	10.11
2003	10.58
2004	11.3
2005	12.34
2006	13.24
2007	14.45
2008	15.88
2009	17.32
2010	18.66
2011	20.25
2012	21.73
2013	23.19
2014	24.75
2015	26.54
2016	28.47