Year	Number of
1990	11.33
1991	11.47
1992	11.48
1993	11.68
1994	11.93
1995	12.06
1996	11.94
1997	10.79
1998	10.16
1999	9.49
2000	8.82
2001	8.13
2002	7.54
2003	7.28
2004	7.06
2005	6.9
2006	6.86
2007	6.83
2008	6.77
2009	6.72
2010	6.71
2011	6.7
2012	6.63
2013	6.61
2014	6.6
2015	6.74
2016	6.91