Year	Number of
1990	31.57
1991	31.58
1992	30.33
1993	29.81
1994	28.71
1995	29.5
1996	28.41
1997	27.64
1998	26.25
1999	22.58
2000	19.96
2001	18.88
2002	18.68
2003	18.98
2004	18.27
2005	18.35
2006	19.07
2007	19.83
2008	20.35
2009	22.17
2010	23.97
2011	24.81
2012	25.88
2013	26.78
2014	27.69
2015	28.56
2016	29.49