Year	Number of
1990	16.83
1991	16.76
1992	16.61
1993	16.47
1994	16.42
1995	16.37
1996	15.78
1997	14.24
1998	13.33
1999	12.42
2000	11.6
2001	10.68
2002	9.91
2003	9.59
2004	9.21
2005	8.99
2006	8.89
2007	8.86
2008	8.86
2009	8.94
2010	9
2011	9.13
2012	9.17
2013	9.28
2014	9.55
2015	9.9
2016	10.27