Year	Number of
1990	5.68
1991	5.96
1992	6.28
1993	6.44
1994	6.52
1995	6.66
1996	6.51
1997	6.51
1998	6.49
1999	6.45
2000	6.4
2001	6.49
2002	6.6
2003	6.63
2004	6.54
2005	6.76
2006	6.81
2007	6.95
2008	7.06
2009	7.3
2010	7.52
2011	7.61
2012	7.66
2013	7.95
2014	8.24
2015	8.38
2016	8.88