Year	Number of
1990	10.94
1991	11.15
1992	11.51
1993	11.56
1994	11.74
1995	11.96
1996	11.98
1997	12.19
1998	12.23
1999	12.32
2000	12.84
2001	13.28
2002	13.53
2003	13.75
2004	14.08
2005	14.03
2006	14.53
2007	15.16
2008	15.59
2009	16.19
2010	16.86
2011	17.21
2012	18.1
2013	18.09
2014	18.74
2015	19.27
2016	19.67