Year	Number of
1990	5.84
1991	5.71
1992	5.82
1993	5.85
1994	5.87
1995	5.87
1996	5.89
1997	6.03
1998	6.1
1999	6.16
2000	6.26
2001	6.44
2002	6.52
2003	6.75
2004	6.87
2005	7.13
2006	7.25
2007	7.14
2008	7.17
2009	7.24
2010	7.24
2011	7.31
2012	7.45
2013	7.65
2014	7.99
2015	8.16
2016	8.31