Year	Number of
1990	2.15
1991	2.13
1992	2.12
1993	2.12
1994	2.12
1995	2.13
1996	2.09
1997	2.05
1998	1.99
1999	1.94
2000	1.9
2001	1.88
2002	1.86
2003	1.84
2004	1.8
2005	1.77
2006	1.77
2007	1.78
2008	1.78
2009	1.79
2010	1.81
2011	1.85
2012	1.91
2013	1.97
2014	2.03
2015	2.1
2016	2.17