Year	Number of
1990	12.55
1991	13.96
1992	15.5
1993	17.14
1994	19.03
1995	21.29
1996	22.69
1997	24.33
1998	25.8
1999	27.32
2000	28.87
2001	29.42
2002	29.98
2003	30.77
2004	31.54
2005	32.28
2006	33.49
2007	34.8
2008	36.79
2009	38.97
2010	41.38
2011	42.96
2012	44.75
2013	46.11
2014	47.67
2015	49.49
2016	51.85