Year	Number of
1990	13.24
1991	14.25
1992	15.14
1993	15.95
1994	16.39
1995	16.42
1996	16.42
1997	16.55
1998	16.64
1999	16.63
2000	16.57
2001	16.67
2002	16.89
2003	17.65
2004	18.85
2005	19.65
2006	20.49
2007	21.39
2008	22.16
2009	22.82
2010	23.34
2011	23.78
2012	24.24
2013	24.7
2014	25.16
2015	25.63
2016	25.81