Year	Number of
1990	31.38
1991	33.95
1992	36.31
1993	38.5
1994	39.83
1995	40.08
1996	40.38
1997	41.08
1998	41.77
1999	42.22
2000	42.48
2001	42.85
2002	43.56
2003	45.68
2004	48.95
2005	51.24
2006	53.4
2007	55.76
2008	57.78
2009	59.49
2010	60.81
2011	61.9
2012	63.04
2013	64.18
2014	65.32
2015	66.48
2016	67.45