Year	Number of
1990	29.19
1991	29.1
1992	28.74
1993	28.05
1994	27.54
1995	27.11
1996	26.98
1997	27.21
1998	27.1
1999	27.49
2000	28.09
2001	29.98
2002	32.72
2003	35.47
2004	38.58
2005	41.78
2006	44.67
2007	47.76
2008	50.57
2009	53.8
2010	57.39
2011	59.7
2012	62.17
2013	64.68
2014	67.15
2015	69.36
2016	72.23