Year	Number of
1990	6.12
1991	6.25
1992	6.38
1993	6.53
1994	6.73
1995	6.93
1996	7.09
1997	7.28
1998	7.37
1999	7.3
2000	7.27
2001	7.15
2002	6.94
2003	6.87
2004	6.66
2005	6.6
2006	6.57
2007	6.45
2008	6.62
2009	6.61
2010	6.77
2011	6.97
2012	7.13
2013	7.27
2014	7.42
2015	7.57
2016	7.74