Year	Number of
1990	2.28
1991	2.35
1992	2.41
1993	2.48
1994	2.55
1995	2.61
1996	2.62
1997	2.63
1998	2.63
1999	2.65
2000	2.64
2001	2.68
2002	2.76
2003	2.79
2004	2.83
2005	2.96
2006	2.99
2007	2.99
2008	2.97
2009	3.02
2010	3.06
2011	3.01
2012	2.98
2013	2.97
2014	3.08
2015	3.12
2016	3.09