Year	Number of
1990	5.79
1991	5.89
1992	6.02
1993	5.72
1994	5.79
1995	5.53
1996	5.24
1997	5.06
1998	5.06
1999	5.04
2000	5.24
2001	5.26
2002	5.29
2003	5.24
2004	5.19
2005	4.93
2006	4.97
2007	4.89
2008	4.79
2009	4.75
2010	4.74
2011	4.67
2012	4.82
2013	4.88
2014	5.17
2015	5.32
2016	5.5