Year	Number of
1990	10.66
1991	10.95
1992	11.21
1993	11.52
1994	11.9
1995	12.33
1996	12.76
1997	13.13
1998	13.49
1999	13.63
2000	13.86
2001	14.12
2002	14.38
2003	14.71
2004	15.07
2005	15.39
2006	15.68
2007	15.89
2008	16.28
2009	16.8
2010	17.44
2011	18
2012	17.81
2013	18.49
2014	19.16
2015	19.91
2016	20.63