Year	Number of
1990	19.04
1991	20.67
1992	22.51
1993	24.49
1994	26.69
1995	29.13
1996	30.71
1997	32.45
1998	34.28
1999	36.4
2000	38.83
2001	39.16
2002	39.64
2003	40.08
2004	40.67
2005	41.4
2006	42.29
2007	43.28
2008	44.55
2009	46.11
2010	47.9
2011	49.56
2012	51.24
2013	53.53
2014	55.98
2015	58.61
2016	61.6