Year	Number of
1990	4.36
1991	4.44
1992	4.47
1993	4.48
1994	4.52
1995	4.58
1996	4.61
1997	4.63
1998	4.72
1999	4.76
2000	4.5
2001	4.43
2002	4.59
2003	4.85
2004	5.12
2005	5.21
2006	5.17
2007	5.13
2008	5.04
2009	5.13
2010	5.21
2011	5.36
2012	5.44
2013	5.61
2014	5.77
2015	5.94
2016	6.08