Year	Number of
1990	3.82
1991	3.84
1992	3.86
1993	3.87
1994	3.89
1995	3.91
1996	3.82
1997	3.75
1998	3.67
1999	3.6
2000	3.54
2001	3.48
2002	3.41
2003	3.34
2004	3.28
2005	3.23
2006	3.3
2007	3.39
2008	3.47
2009	3.55
2010	3.62
2011	3.69
2012	3.77
2013	3.84
2014	3.91
2015	3.99
2016	4.07