Year	Number of
1990	13.31
1991	13.43
1992	13.83
1993	13.88
1994	14.46
1995	15.32
1996	16.28
1997	16.62
1998	17.34
1999	18.03
2000	18.77
2001	18.75
2002	19.14
2003	19.45
2004	19.53
2005	19.39
2006	19.15
2007	18.79
2008	19.06
2009	19.31
2010	19.32
2011	19.33
2012	19.06
2013	19.33
2014	19.6
2015	19.85
2016	20.18