Year	Number of
1990	54.96
1991	56.31
1992	57.86
1993	59.53
1994	61.33
1995	63.26
1996	65.35
1997	67.56
1998	69.8
1999	71.99
2000	74.1
2001	76.63
2002	78.97
2003	81.4
2004	84.05
2005	87.08
2006	91.32
2007	96.17
2008	101.61
2009	107.5
2010	113.83
2011	118.09
2012	122.52
2013	127
2014	131.76
2015	136.85
2016	142.06