Year	Number of
1990	17.77
1991	17.67
1992	17.46
1993	17.37
1994	17.3
1995	17.15
1996	16.95
1997	15.58
1998	14.86
1999	14.11
2000	13.41
2001	12.35
2002	11.43
2003	11.09
2004	10.49
2005	10.27
2006	10.34
2007	10.25
2008	10.18
2009	10.45
2010	10.33
2011	10.21
2012	10.16
2013	10.21
2014	10.72
2015	11.08
2016	11.6