Year	Number of
1990	6.47
1991	6.99
1992	7.27
1993	7.55
1994	7.84
1995	8.28
1996	8.41
1997	8.54
1998	8.65
1999	9.07
2000	9.31
2001	9.75
2002	10.14
2003	10.48
2004	10.69
2005	11.03
2006	11.5
2007	11.93
2008	12.83
2009	13.91
2010	15.09
2011	16.01
2012	16.82
2013	17.29
2014	18.15
2015	18.54
2016	19.43