Year	Number of
1990	21.74
1991	22.54
1992	23.63
1993	24.81
1994	26.1
1995	27.36
1996	28.17
1997	28.86
1998	29.47
1999	30.43
2000	31.35
2001	32.07
2002	33.7
2003	36.17
2004	38.83
2005	41.12
2006	42.93
2007	44.15
2008	47.17
2009	50.72
2010	53.28
2011	55.72
2012	58.13
2013	60.37
2014	62.71
2015	65.07
2016	67.41