Year	Number of
1990	25.87
1991	25.74
1992	25.33
1993	24.79
1994	24.29
1995	23.84
1996	23.8
1997	23.9
1998	24.14
1999	24.8
2000	25.71
2001	27.54
2002	29.92
2003	32.63
2004	35.55
2005	38.59
2006	41.08
2007	43.53
2008	45.93
2009	48.44
2010	51.15
2011	52.61
2012	54.23
2013	56.02
2014	57.79
2015	59.4
2016	61.26