Year	Number of
1990	14.12
1991	14.43
1992	14.68
1993	14.88
1994	14.68
1995	14.25
1996	14.09
1997	14.12
1998	14.46
1999	14.79
2000	15.1
2001	15.41
2002	15.79
2003	15.98
2004	16.04
2005	16.08
2006	16.2
2007	16.44
2008	16.71
2009	16.93
2010	17.24
2011	17.46
2012	17.67
2013	17.97
2014	18.32
2015	18.47
2016	18.73