Year	Number of
1990	21.2
1991	23.11
1992	25.23
1993	27.31
1994	29.65
1995	32.19
1996	34.48
1997	36.9
1998	39.14
1999	41.52
2000	43.95
2001	46.08
2002	48.69
2003	51.84
2004	57.05
2005	65.93
2006	73.92
2007	84.94
2008	97.83
2009	113.64
2010	129.04
2011	146.83
2012	162.83
2013	177.89
2014	193.21
2015	209.66
2016	227.61