Year	Number of
1990	2.43
1991	2.44
1992	2.43
1993	2.4
1994	2.4
1995	2.41
1996	2.42
1997	2.4
1998	2.42
1999	2.39
2000	2.37
2001	2.35
2002	2.31
2003	2.23
2004	2.15
2005	2.11
2006	2.07
2007	1.98
2008	1.93
2009	1.97
2010	2.03
2011	2.02
2012	2.02
2013	2.09
2014	2.1
2015	2.11
2016	2.15