Year	Number of
1990	4.43
1991	4.6
1992	4.81
1993	5.04
1994	5.27
1995	5.47
1996	5.81
1997	6.03
1998	6.14
1999	6.21
2000	6.38
2001	6.35
2002	6.37
2003	6.33
2004	6.4
2005	6.3
2006	6.28
2007	6.22
2008	6.09
2009	6.11
2010	6.15
2011	6.08
2012	6.17
2013	6.07
2014	6.04
2015	6.03
2016	6.05