Year	Number of
1990	9.25
1991	9.85
1992	10.17
1993	10.43
1994	10.72
1995	11.08
1996	11.21
1997	11.41
1998	11.7
1999	12.47
2000	12.96
2001	13.11
2002	12.77
2003	12.75
2004	12.98
2005	13.13
2006	13.49
2007	14.03
2008	14.99
2009	15.92
2010	16.88
2011	17.23
2012	17.24
2013	17.22
2014	17.99
2015	18.37
2016	19.21