Year	Number of
1990	6.25
1991	6.28
1992	6.33
1993	6.41
1994	6.35
1995	6.46
1996	6.71
1997	6.91
1998	7.19
1999	7.29
2000	7.38
2001	7.58
2002	7.75
2003	7.93
2004	8.1
2005	8.28
2006	8.36
2007	8.26
2008	8.32
2009	8.43
2010	8.4
2011	8.56
2012	9.03
2013	9.08
2014	9.25
2015	9.49
2016	9.8