Year	Number of
1990	45.87
1991	45.93
1992	45.77
1993	46.21
1994	47.41
1995	48.66
1996	52.93
1997	57.89
1998	64.62
1999	71.55
2000	79.41
2001	84.79
2002	89.8
2003	92.76
2004	96.63
2005	100.68
2006	106.97
2007	113.93
2008	121.63
2009	129.65
2010	137.45
2011	145.26
2012	152.16
2013	158.42
2014	164.25
2015	170.51
2016	178.74