Year	Number of
1990	2.09
1991	2.11
1992	2.12
1993	2.15
1994	2.13
1995	2.08
1996	2.08
1997	2
1998	1.98
1999	1.89
2000	1.88
2001	1.71
2002	1.67
2003	1.63
2004	1.58
2005	1.55
2006	1.54
2007	1.49
2008	1.48
2009	1.48
2010	1.53
2011	1.51
2012	1.57
2013	1.63
2014	1.7
2015	1.85
2016	1.9