Year	Number of
1990	5.21
1991	5.17
1992	5.05
1993	4.91
1994	4.8
1995	4.76
1996	4.97
1997	4.87
1998	4.97
1999	4.81
2000	4.7
2001	4.69
2002	4.6
2003	4.6
2004	4.62
2005	4.43
2006	4.3
2007	4.15
2008	4.13
2009	4.36
2010	4.52
2011	4.42
2012	4.45
2013	4.64
2014	4.83
2015	4.99
2016	5.16