Year	Number of
1990	23.38
1991	22.52
1992	21.43
1993	20.18
1994	18.99
1995	17.88
1996	16.84
1997	16.49
1998	15.94
1999	14.96
2000	14.58
2001	14.04
2002	13.53
2003	13.31
2004	13.23
2005	13.29
2006	13.09
2007	12.94
2008	12.82
2009	12.78
2010	12.88
2011	12.91
2012	13.02
2013	13.17
2014	13.32
2015	13.45
2016	13.6