Year	Number of
1990	25.82
1991	26.98
1992	28.32
1993	29.83
1994	31.5
1995	33.32
1996	34.71
1997	36
1998	36.9
1999	37.85
2000	39.06
2001	40.24
2002	41.49
2003	42.53
2004	43.28
2005	43.9
2006	44.96
2007	46.13
2008	47.02
2009	48.16
2010	49.56
2011	51.13
2012	52.97
2013	54.97
2014	57.03
2015	59.21
2016	61.99