Year	Number of
1990	172.13
1991	169.51
1992	169.16
1993	166.76
1994	165.48
1995	162.24
1996	154.69
1997	151.51
1998	147.27
1999	144.24
2000	141.65
2001	140.46
2002	138.93
2003	137.46
2004	136.01
2005	134.59
2006	139.62
2007	144.17
2008	147.7
2009	150.71
2010	153.5
2011	156.09
2012	158.62
2013	161.32
2014	166.1
2015	171.57
2016	176.93