Year	Number of
1990	3.07
1991	3.07
1992	3.1
1993	3.17
1994	3.23
1995	3.27
1996	3.15
1997	3.01
1998	2.87
1999	2.74
2000	2.64
2001	2.68
2002	2.73
2003	2.76
2004	2.79
2005	2.81
2006	2.81
2007	2.8
2008	2.79
2009	2.79
2010	2.81
2011	2.89
2012	2.99
2013	3.08
2014	3.16
2015	3.24
2016	3.35