Year	Number of
1990	3.22
1991	3.17
1992	3.17
1993	3.2
1994	3.21
1995	3.22
1996	3.27
1997	3.15
1998	3.03
1999	2.9
2000	2.82
2001	2.74
2002	2.78
2003	2.8
2004	2.79
2005	2.83
2006	2.83
2007	2.78
2008	2.74
2009	2.74
2010	2.83
2011	2.86
2012	3.03
2013	3.17
2014	3.37
2015	3.73
2016	3.66