Year	Number of
1990	2.46
1991	2.5
1992	2.61
1993	2.56
1994	2.6
1995	2.59
1996	2.43
1997	2.24
1998	2.23
1999	2.15
2000	2.21
2001	2.14
2002	2.2
2003	2.2
2004	2.24
2005	2.22
2006	2.28
2007	2.3
2008	2.31
2009	2.32
2010	2.36
2011	2.43
2012	2.56
2013	2.63
2014	2.84
2015	2.87
2016	2.94