Year	Number of
1990	14.55
1991	14.92
1992	15.38
1993	15.94
1994	16.63
1995	17.3
1996	17.92
1997	18.46
1998	18.83
1999	19.08
2000	18.92
2001	18.75
2002	18.53
2003	18.36
2004	18.47
2005	18.36
2006	18.03
2007	17.43
2008	16.99
2009	16.94
2010	17.15
2011	17.58
2012	17.93
2013	17.98
2014	17.87
2015	17.73
2016	17.7