Year	Number of
1990	10.78
1991	10.81
1992	10.88
1993	10.79
1994	10.82
1995	10.94
1996	11.08
1997	11.23
1998	11.24
1999	11.09
2000	11.17
2001	11.47
2002	11.54
2003	11.6
2004	11.95
2005	12.38
2006	12.95
2007	13.55
2008	14.02
2009	14.51
2010	14.95
2011	15.37
2012	15.84
2013	16.27
2014	16.99
2015	17.54
2016	18.48