Year	Number of
1990	9.73
1991	9.59
1992	9.43
1993	9.23
1994	9.16
1995	9.38
1996	9.93
1997	10.21
1998	9.99
1999	9.76
2000	9.52
2001	9.38
2002	9.14
2003	8.81
2004	8.67
2005	8.57
2006	8.1
2007	7.74
2008	7.69
2009	7.71
2010	7.46
2011	7.04
2012	6.57
2013	6.3
2014	6.29
2015	6.37
2016	6.51