Year	Number of
1990	5.05
1991	5.14
1992	5.25
1993	5.23
1994	5.3
1995	5.28
1996	5.22
1997	5.59
1998	6.15
1999	6.35
2000	6.46
2001	6.48
2002	6.37
2003	6.21
2004	6.1
2005	5.89
2006	5.89
2007	5.76
2008	6.01
2009	6.08
2010	6.11
2011	6.23
2012	6.51
2013	6.65
2014	6.84
2015	6.98
2016	7.15