Year	Number of
1990	54.09
1991	53.96
1992	53.35
1993	52.37
1994	51.3
1995	50.31
1996	49.83
1997	49.5
1998	49.44
1999	49.71
2000	50.33
2001	52.33
2002	54.93
2003	57.99
2004	61.15
2005	64.25
2006	66.63
2007	68.72
2008	70.69
2009	72.67
2010	74.81
2011	77.36
2012	80.04
2013	82.75
2014	85.56
2015	88.48
2016	91.94