Year	Number of
1990	60.49
1991	61.98
1992	63.62
1993	65.33
1994	67.08
1995	69.09
1996	72.08
1997	75.36
1998	78.89
1999	82.67
2000	86.74
2001	89.78
2002	93.05
2003	96.58
2004	100.54
2005	104.92
2006	110.22
2007	115.78
2008	121.82
2009	128.28
2010	135.36
2011	140.68
2012	146.42
2013	152.48
2014	159.06
2015	165.71
2016	172.75