Year	Number of
1990	6.15
1991	5.76
1992	5.45
1993	6.76
1994	7.36
1995	6.89
1996	7.14
1997	7.19
1998	7.3
1999	7.39
2000	7.61
2001	7.72
2002	8.05
2003	8.49
2004	8.64
2005	9.1
2006	9.23
2007	9.24
2008	9.81
2009	9.97
2010	9.89
2011	10.14
2012	9.93
2013	9.91
2014	9.06
2015	9.84
2016	9.61