Year	Number of
1990	28.11
1991	30.59
1992	33.29
1993	36.33
1994	39.7
1995	43.47
1996	46.37
1997	49.54
1998	53.1
1999	56.75
2000	60.45
2001	64.75
2002	69.2
2003	73.9
2004	79.07
2005	84.9
2006	90.03
2007	95.72
2008	101.91
2009	108.59
2010	115.77
2011	120.63
2012	125.73
2013	131.04
2014	136.7
2015	142.74
2016	149.1