Year	Number of
1990	5.93
1991	6.12
1992	6.33
1993	6.39
1994	6.47
1995	6.55
1996	6.45
1997	6.4
1998	6.54
1999	6.73
2000	6.78
2001	6.83
2002	7.11
2003	6.93
2004	7.02
2005	7.1
2006	7.27
2007	7.54
2008	7.62
2009	7.9
2010	7.97
2011	8.03
2012	8.37
2013	8.61
2014	8.85
2015	9.12
2016	9.4