Year	Number of
1990	2.82
1991	2.8
1992	2.76
1993	2.66
1994	2.73
1995	2.69
1996	2.68
1997	2.56
1998	2.53
1999	2.55
2000	2.55
2001	2.5
2002	2.51
2003	2.44
2004	2.35
2005	2.23
2006	2.16
2007	2.02
2008	2.02
2009	2
2010	2.02
2011	2.01
2012	1.99
2013	1.99
2014	2.11
2015	2.16
2016	2.23