Year	Number of
1990	23.2
1991	24.01
1992	24.84
1993	25.68
1994	26.52
1995	27.36
1996	28.85
1997	30.31
1998	31.85
1999	33.4
2000	35.02
2001	36.96
2002	39.04
2003	41.25
2004	43.6
2005	46.11
2006	47.33
2007	48.45
2008	49.27
2009	50.04
2010	50.8
2011	51.66
2012	52.64
2013	53.43
2014	54.26
2015	55.09
2016	56.52