Year	Number of
1990	16.27
1991	16.78
1992	17.19
1993	18.01
1994	17.52
1995	17.95
1996	17.18
1997	17.65
1998	18.32
1999	20.27
2000	20.9
2001	22.52
2002	23.07
2003	22.8
2004	22.61
2005	20.87
2006	22.33
2007	22.52
2008	21.9
2009	21.03
2010	19.99
2011	19.5
2012	18.96
2013	17.41
2014	16.49
2015	16.67
2016	16.65