Year	Number of
1990	8.42
1991	8.82
1992	9.35
1993	10.07
1994	10.56
1995	10.8
1996	11.88
1997	12.22
1998	12.57
1999	13.31
2000	13.59
2001	13.56
2002	13.77
2003	13.66
2004	13.43
2005	13.18
2006	13.51
2007	13.7
2008	13.93
2009	14.18
2010	14.35
2011	14.35
2012	14.58
2013	14.73
2014	15.11
2015	15.18
2016	15.88