Year	Number of
1990	17.2
1991	17.44
1992	17.64
1993	17.78
1994	17.76
1995	17.55
1996	16.96
1997	16.42
1998	15.8
1999	15.22
2000	14.85
2001	14.75
2002	15.1
2003	15.83
2004	15.55
2005	14.96
2006	14.56
2007	14.68
2008	15.05
2009	15.45
2010	16.07
2011	16.07
2012	16.06
2013	16.17
2014	16.48
2015	16.88
2016	17.16