Year	Number of
1990	5.43
1991	5.77
1992	5.91
1993	6.02
1994	6.19
1995	6.26
1996	6.91
1997	7.61
1998	8.39
1999	9.19
2000	9.84
2001	9.92
2002	10.13
2003	10.44
2004	11.06
2005	12.6
2006	12.76
2007	13.35
2008	14.01
2009	14.72
2010	15.04
2011	15.17
2012	15.49
2013	15.98
2014	16.36
2015	17.06
2016	18.74