Year	Number of
1990	24.98
1991	25.89
1992	26.98
1993	28.15
1994	29.42
1995	30.84
1996	32.57
1997	34.38
1998	36.21
1999	38.27
2000	40.87
2001	43.49
2002	45.9
2003	47.8
2004	49.75
2005	52.03
2006	54.27
2007	56.24
2008	58.52
2009	60.36
2010	62.34
2011	64.39
2012	65.63
2013	67.38
2014	68.73
2015	69.99
2016	72.27