Year	Number of
1990	66.55
1991	69.02
1992	71.58
1993	74.27
1994	77.12
1995	80.21
1996	83.32
1997	86.67
1998	90.26
1999	94.05
2000	98.11
2001	101.96
2002	106.11
2003	110.56
2004	115.26
2005	120.3
2006	124.45
2007	128.65
2008	133.17
2009	137.9
2010	142.98
2011	147.25
2012	151.83
2013	156.57
2014	161.52
2015	166.72
2016	172.42