Year	Number of
1990	9.61
1991	9.65
1992	9.68
1993	9.71
1994	9.75
1995	9.82
1996	9.48
1997	9.19
1998	8.88
1999	8.59
2000	8.33
2001	8.1
2002	7.89
2003	7.68
2004	7.48
2005	7.3
2006	7.31
2007	7.34
2008	7.37
2009	7.41
2010	7.46
2011	7.67
2012	7.9
2013	8.13
2014	8.37
2015	8.61
2016	8.87