Year	Number of
1990	35.5
1991	35.87
1992	36.21
1993	36.31
1994	36.7
1995	37.48
1996	38.18
1997	39.13
1998	40.26
1999	41.2
2000	41.9
2001	42.88
2002	43.81
2003	45.37
2004	47.09
2005	49.03
2006	50.47
2007	51.96
2008	53.47
2009	55.03
2010	56.68
2011	58.46
2012	60.39
2013	62.29
2014	64.35
2015	66.62
2016	68.79