Year	Number of
1990	19.64
1991	20.36
1992	21.21
1993	22.13
1994	23.2
1995	24.27
1996	24.78
1997	25.37
1998	25.92
1999	27.16
2000	28.86
2001	31.58
2002	34.49
2003	37.27
2004	40.99
2005	45.03
2006	47.23
2007	49.81
2008	53.2
2009	56.56
2010	59.38
2011	61.71
2012	62.46
2013	62.74
2014	63.47
2015	63.48
2016	63.76