Year	Number of
1990	19.28
1991	20.21
1992	21.32
1993	22.6
1994	23.83
1995	24.88
1996	26.46
1997	28.01
1998	29.59
1999	31.48
2000	33.81
2001	35.39
2002	37.23
2003	39.24
2004	41.19
2005	43.05
2006	44.27
2007	45.42
2008	46.63
2009	48.22
2010	50.31
2011	51.64
2012	53.3
2013	54.7
2014	56.16
2015	57.62
2016	59.56