Year	Number of
1990	10.99
1991	11.07
1992	11.36
1993	11.42
1994	11.87
1995	12.56
1996	13.34
1997	13.71
1998	14.38
1999	15.13
2000	15.9
2001	15.97
2002	16.29
2003	16.59
2004	16.65
2005	16.48
2006	16.16
2007	15.73
2008	15.86
2009	16.1
2010	15.91
2011	15.79
2012	15.54
2013	15.69
2014	15.82
2015	16.01
2016	16.29