Year	Number of
1990	28.11
1991	28.07
1992	27.64
1993	26.72
1994	25.1
1995	22.56
1996	19.31
1997	16.99
1998	16.28
1999	16.32
2000	16.5
2001	16.65
2002	16.84
2003	17.27
2004	17.68
2005	17.95
2006	18.07
2007	18.03
2008	18.3
2009	18.68
2010	19.09
2011	19.19
2012	20.04
2013	20.24
2014	20.57
2015	21.03
2016	21.62