Year	Number of
1990	27.17
1991	27.02
1992	26.51
1993	25.51
1994	23.76
1995	21.09
1996	17.82
1997	15.61
1998	14.98
1999	15.07
2000	15.25
2001	15.35
2002	15.49
2003	15.81
2004	16.1
2005	16.3
2006	16.32
2007	16.24
2008	16.36
2009	16.57
2010	16.78
2011	16.8
2012	17.45
2013	17.59
2014	17.83
2015	18.16
2016	18.6