Year	Number of
1990	2.27
1991	2.25
1992	2.25
1993	2.26
1994	2.24
1995	2.22
1996	2.21
1997	2.12
1998	2.09
1999	1.98
2000	2
2001	1.89
2002	1.88
2003	1.87
2004	1.85
2005	1.86
2006	1.86
2007	1.81
2008	1.8
2009	1.8
2010	1.88
2011	1.94
2012	1.98
2013	2.01
2014	2.1
2015	2.16
2016	2.24