Year	Number of
1990	12.45
1991	12.27
1992	11.98
1993	11.62
1994	11.26
1995	10.94
1996	10.36
1997	10.47
1998	10.56
1999	10.36
2000	10.82
2001	10.9
2002	11.04
2003	11.49
2004	11.72
2005	12.09
2006	12.33
2007	12.63
2008	12.87
2009	13.39
2010	13.75
2011	14.07
2012	14.49
2013	14.94
2014	15.38
2015	15.78
2016	16.21