Year	Number of
1990	9.83
1991	8.72
1992	8.02
1993	8.11
1994	8.12
1995	8.98
1996	9.36
1997	9.65
1998	10.02
1999	10.87
2000	11.45
2001	10.9
2002	10.92
2003	10.15
2004	10.02
2005	10.82
2006	11.14
2007	12.16
2008	13.22
2009	13.89
2010	13.92
2011	13.4
2012	13.73
2013	13.33
2014	14.78
2015	15.96
2016	17.49