Year	Number of
1990	14.66
1991	14.96
1992	15.31
1993	15.72
1994	16.25
1995	16.8
1996	17.31
1997	17.78
1998	18.15
1999	18.41
2000	18.33
2001	18.23
2002	18.15
2003	18.08
2004	18.32
2005	18.34
2006	18.11
2007	17.63
2008	17.31
2009	17.33
2010	17.62
2011	18.08
2012	18.46
2013	18.6
2014	18.59
2015	18.56
2016	18.64