Year	Number of
1990	14.58
1991	14.51
1992	14.41
1993	14.41
1994	14.1
1995	13.79
1996	13.47
1997	13.35
1998	13.04
1999	12.8
2000	12.61
2001	12.47
2002	12.32
2003	12.17
2004	12
2005	11.86
2006	11.84
2007	11.72
2008	11.6
2009	11.5
2010	11.64
2011	11.74
2012	11.69
2013	11.97
2014	12.28
2015	12.64
2016	12.84