Year	Number of
1990	26.16
1991	25.72
1992	25.89
1993	25.54
1994	25.31
1995	24.64
1996	25.04
1997	25.23
1998	25.45
1999	23.55
2000	22.57
2001	21.08
2002	21.04
2003	21.46
2004	21.68
2005	22.05
2006	21.96
2007	21.45
2008	21.86
2009	21.61
2010	22.09
2011	22.23
2012	22.12
2013	22.98
2014	23.44
2015	23.92
2016	23.86