Year	Number of
1990	35.2
1991	36
1992	35.61
1993	38.09
1994	39.05
1995	41.21
1996	43.33
1997	43.81
1998	44.5
1999	46.02
2000	47.52
2001	48.81
2002	51.72
2003	55.1
2004	59.64
2005	63.6
2006	65.01
2007	65.99
2008	67.4
2009	68.69
2010	70.55
2011	72.53
2012	74.32
2013	75.75
2014	77.57
2015	79.35
2016	81.26