Year	Number of
1990	5.78
1991	6.16
1992	6.48
1993	6.73
1994	6.88
1995	7.49
1996	8.04
1997	8.01
1998	8.35
1999	8.67
2000	8.94
2001	9.08
2002	9.12
2003	9.43
2004	9.8
2005	10.23
2006	10.73
2007	11.36
2008	11.98
2009	12.85
2010	13.77
2011	14.14
2012	14.56
2013	14.96
2014	15.41
2015	15.86
2016	16.21