Year	Number of
1990	15.62
1991	16.04
1992	15.58
1993	15.11
1994	15.46
1995	15.4
1996	15.93
1997	15.95
1998	15.98
1999	15.62
2000	15.52
2001	15.65
2002	16.19
2003	16.02
2004	15.06
2005	14.33
2006	13.9
2007	13.57
2008	14.15
2009	14.05
2010	14.72
2011	14.7
2012	13.96
2013	13.88
2014	13.65
2015	13.52
2016	13.12