Year	Number of
1990	70.55
1991	70.52
1992	70.23
1993	69.94
1994	70.32
1995	71.4
1996	73.35
1997	76.52
1998	80.64
1999	83.67
2000	86.13
2001	87.42
2002	88.88
2003	90.68
2004	92.47
2005	94.59
2006	96.33
2007	98.61
2008	101.75
2009	105.36
2010	109.55
2011	113.6
2012	117.97
2013	122.74
2014	127.88
2015	133.24
2016	137.84