Year	Number of
1990	1.71
1991	1.78
1992	1.87
1993	1.87
1994	1.88
1995	1.86
1996	1.77
1997	1.67
1998	1.7
1999	1.64
2000	1.68
2001	1.55
2002	1.58
2003	1.51
2004	1.48
2005	1.45
2006	1.41
2007	1.34
2008	1.32
2009	1.3
2010	1.28
2011	1.27
2012	1.26
2013	1.26
2014	1.29
2015	1.3
2016	1.34