Year	Number of
1990	10.46
1991	10.51
1992	10.55
1993	10.66
1994	10.64
1995	10.61
1996	10.77
1997	11.15
1998	11.15
1999	11.15
2000	11.07
2001	11.31
2002	11.58
2003	12.03
2004	12.13
2005	12.17
2006	12.18
2007	12.29
2008	12.58
2009	12.9
2010	13.19
2011	13.57
2012	14.16
2013	14.66
2014	15.17
2015	15.56
2016	15.98