Year	Number of
1990	17.92
1991	18.36
1992	19.01
1993	19.48
1994	20.4
1995	21.51
1996	23.04
1997	24.24
1998	25.83
1999	27.79
2000	29.86
2001	29.57
2002	29.42
2003	30.27
2004	30.56
2005	30.5
2006	30.1
2007	29.48
2008	28.87
2009	27.87
2010	27.79
2011	27.92
2012	27.97
2013	28.48
2014	29.03
2015	29.68
2016	30.37