Year	Number of
1990	5.3
1991	5.64
1992	5.98
1993	6.39
1994	6.77
1995	7.08
1996	7.38
1997	7.59
1998	7.81
1999	8.12
2000	8.52
2001	9.08
2002	9.83
2003	10.79
2004	11.69
2005	12.42
2006	13.88
2007	15.34
2008	17.28
2009	19.45
2010	21.91
2011	23.27
2012	24.7
2013	25.74
2014	27.04
2015	28.57
2016	30.13