Year	Number of
1990	26.72
1991	26.66
1992	26.9
1993	25.96
1994	26.04
1995	25.08
1996	24.36
1997	23.14
1998	22.38
1999	20.48
2000	19.69
2001	17.8
2002	18.51
2003	17.37
2004	17.46
2005	17.61
2006	17.91
2007	18.32
2008	18.57
2009	20.28
2010	19.91
2011	20.99
2012	21.8
2013	22.52
2014	23.26
2015	23.97
2016	24.71