Year	Number of
1990	13.68
1991	14.83
1992	15.67
1993	16.45
1994	17.42
1995	18.55
1996	18.33
1997	18.37
1998	18.47
1999	18.82
2000	19.34
2001	18.52
2002	20.04
2003	21.5
2004	23.81
2005	27.58
2006	29.17
2007	32.47
2008	38.2
2009	43.3
2010	49.48
2011	52.41
2012	55.37
2013	58.29
2014	60.69
2015	62.55
2016	68.18