Year	Number of
1990	24.44
1991	25.06
1992	25.73
1993	26.46
1994	27.24
1995	28.08
1996	28.92
1997	29.82
1998	30.8
1999	31.87
2000	33.05
2001	33.98
2002	35.01
2003	36.13
2004	37.33
2005	38.61
2006	39.73
2007	40.9
2008	42.15
2009	43.5
2010	44.96
2011	46.47
2012	48.09
2013	49.76
2014	51.55
2015	53.47
2016	55.58