Year	Number of
1990	5.64
1991	5.37
1992	5.25
1993	5.13
1994	5.03
1995	4.97
1996	5.04
1997	4.99
1998	4.9
1999	4.81
2000	4.76
2001	4.69
2002	4.73
2003	4.75
2004	4.68
2005	4.64
2006	4.6
2007	4.46
2008	4.38
2009	4.36
2010	4.36
2011	4.41
2012	4.51
2013	4.57
2014	4.68
2015	4.72
2016	4.79