Year	Number of
1990	25.9
1991	26.73
1992	27.6
1993	28.54
1994	29.61
1995	30.84
1996	32.5
1997	34.43
1998	36.62
1999	38.94
2000	41.39
2001	42.56
2002	43.65
2003	44.33
2004	44.89
2005	45.1
2006	44.88
2007	44.99
2008	45.62
2009	45.72
2010	46.11
2011	46.99
2012	48.58
2013	49.77
2014	51.3
2015	52.88
2016	54.44