Year	Number of
1990	19.61
1991	20.71
1992	21.97
1993	23.38
1994	25
1995	26.79
1996	28.3
1997	29.93
1998	31.57
1999	33.23
2000	34.97
2001	36.86
2002	38.98
2003	41.72
2004	45.61
2005	50.98
2006	56.09
2007	62.95
2008	71.09
2009	79.78
2010	88.57
2011	99.24
2012	109.58
2013	119.99
2014	131.11
2015	143.63
2016	156.45