Year	Number of
1990	68.17
1991	67.94
1992	67.31
1993	66.68
1994	66.46
1995	66.96
1996	68.64
1997	71.49
1998	75.4
1999	79.62
2000	83.91
2001	87.59
2002	91.39
2003	95.54
2004	100.07
2005	105.12
2006	110.11
2007	115.46
2008	121.65
2009	128.37
2010	135.73
2011	143.24
2012	151.46
2013	160.15
2014	169.07
2015	178.1
2016	186.95