Year	Number of
1990	21.69
1991	22.61
1992	23.65
1993	24.84
1994	26.15
1995	27.62
1996	29.51
1997	31.65
1998	33.99
1999	36.41
2000	38.9
2001	42.02
2002	45.2
2003	48.55
2004	52.2
2005	56.32
2006	58.43
2007	60.7
2008	63.41
2009	66.24
2010	69.21
2011	71.68
2012	74.32
2013	77.21
2014	80.29
2015	83.59
2016	87.37