Year	Number of
1990	30.03
1991	29.15
1992	28.6
1993	28.29
1994	27.41
1995	26.7
1996	25.78
1997	25.58
1998	24.53
1999	23.53
2000	22.2
2001	21.94
2002	21.71
2003	22.08
2004	21.06
2005	20.15
2006	19.58
2007	19.29
2008	18.95
2009	18.9
2010	19.15
2011	19.77
2012	20
2013	19.77
2014	20.45
2015	20.87
2016	21.3