Year	Number of
1990	56.4
1991	57.71
1992	59.62
1993	61.17
1994	63.13
1995	65.39
1996	67.39
1997	69.18
1998	70.91
1999	72.8
2000	74.71
2001	76.23
2002	78.09
2003	81.92
2004	86.43
2005	90.34
2006	93.8
2007	97.19
2008	102.72
2009	108.15
2010	113.1
2011	117.5
2012	122.49
2013	127.72
2014	132.99
2015	138.25
2016	144.49