Year	Number of
1990	25.7
1991	26.35
1992	26.97
1993	27.57
1994	28.18
1995	28.85
1996	29.98
1997	31.2
1998	32.49
1999	33.84
2000	35.3
2001	36.87
2002	38.54
2003	40.3
2004	42.24
2005	44.4
2006	45.99
2007	47.67
2008	49.47
2009	51.49
2010	53.76
2011	55.77
2012	57.95
2013	60.18
2014	62.64
2015	65.34
2016	68.55