Year	Number of
1990	52.21
1991	54.31
1992	56.51
1993	58.83
1994	61.33
1995	64.06
1996	66.62
1997	69.39
1998	72.44
1999	75.56
2000	78.8
2001	81.53
2002	84.43
2003	87.75
2004	91.27
2005	95.1
2006	98.27
2007	101.51
2008	105.17
2009	109.02
2010	113.16
2011	116.96
2012	121.09
2013	125.47
2014	130.17
2015	135.19
2016	140.46