Year	Number of
1990	15.82
1991	16.3
1992	16.78
1993	17.26
1994	17.78
1995	18.38
1996	19.27
1997	20.21
1998	21.23
1999	22.24
2000	23.24
2001	24.74
2002	26.27
2003	27.94
2004	29.75
2005	31.77
2006	33.96
2007	36.36
2008	39.04
2009	41.95
2010	45.12
2011	47.38
2012	49.8
2013	52.36
2014	55.13
2015	58.1
2016	61.33