Year	Number of
1990	8.75
1991	8.89
1992	9.02
1993	9.18
1994	9.38
1995	9.62
1996	9.8
1997	10.08
1998	10.03
1999	9.58
2000	9.53
2001	9.26
2002	9.31
2003	9.07
2004	9.16
2005	9.23
2006	9.46
2007	9.63
2008	9.85
2009	9.96
2010	10.06
2011	10.43
2012	10.64
2013	10.82
2014	11.02
2015	11.24
2016	11.51