Year	Number of
1990	4.41
1991	4.7
1992	4.87
1993	5.02
1994	5.21
1995	5.32
1996	5.94
1997	6.62
1998	7.37
1999	8.24
2000	8.99
2001	9.22
2002	9.75
2003	10.4
2004	11.39
2005	13.19
2006	14.3
2007	16.52
2008	18.77
2009	20.86
2010	22.56
2011	23.86
2012	25.48
2013	27.69
2014	30.26
2015	30.91
2016	33.42