Year	Number of
1990	9.49
1991	8.31
1992	7.52
1993	7.6
1994	7.34
1995	6.95
1996	7.03
1997	7.39
1998	7.42
1999	7.78
2000	8.12
2001	8.39
2002	8.84
2003	9.45
2004	10.07
2005	10.86
2006	11.34
2007	11.96
2008	12.66
2009	12.86
2010	12.32
2011	12.15
2012	11.83
2013	11.52
2014	12.32
2015	13.59
2016	14.86