Year	Number of
1990	5.96
1991	5.79
1992	5.93
1993	5.97
1994	6.04
1995	6.12
1996	6.21
1997	6.37
1998	6.47
1999	6.57
2000	6.69
2001	6.88
2002	6.98
2003	7.24
2004	7.37
2005	7.66
2006	7.8
2007	7.71
2008	7.68
2009	7.76
2010	7.73
2011	7.82
2012	7.99
2013	8.19
2014	8.54
2015	8.73
2016	8.86