Year	Number of
1990	7.59
1991	7.83
1992	8.08
1993	8.35
1994	8.63
1995	8.95
1996	9.2
1997	9.52
1998	9.58
1999	9.46
2000	9.66
2001	9.71
2002	10.04
2003	10.14
2004	10.49
2005	10.85
2006	11.4
2007	11.92
2008	12.49
2009	12.96
2010	13.44
2011	14.18
2012	14.77
2013	15.33
2014	15.93
2015	16.57
2016	17.3