Year	Number of
1990	19.38
1991	20.5
1992	21.64
1993	22.71
1994	23.62
1995	24.29
1996	23.61
1997	22.67
1998	22.07
1999	21.52
2000	21.32
2001	22.47
2002	24.29
2003	26.47
2004	28.42
2005	29.86
2006	32.18
2007	34.2
2008	36.63
2009	39.4
2010	42.41
2011	43.87
2012	45.42
2013	46.36
2014	47.6
2015	49.1
2016	50.16