Year	Number of
1990	7.46
1991	7.82
1992	7.98
1993	8.16
1994	8.32
1995	8.47
1996	8.49
1997	8.42
1998	8.36
1999	8.62
2000	8.68
2001	8.63
2002	8.6
2003	8.59
2004	8.56
2005	8.55
2006	8.5
2007	8.51
2008	8.44
2009	8.43
2010	8.49
2011	8.52
2012	8.61
2013	8.66
2014	8.72
2015	8.78
2016	8.83