Year	Number of
1990	24.1
1991	24.6
1992	25.28
1993	26.04
1994	26.89
1995	27.52
1996	28.45
1997	29.36
1998	31.28
1999	32.92
2000	35.67
2001	37.4
2002	39.68
2003	42.83
2004	45.35
2005	48.48
2006	47.93
2007	47.96
2008	48.66
2009	48.64
2010	49.2
2011	50
2012	51.23
2013	52.55
2014	53.46
2015	54.33
2016	54.98