Year	Number of
1990	16.71
1991	16.97
1992	17.08
1993	17.22
1994	17.53
1995	17.91
1996	18.56
1997	19.33
1998	20.22
1999	20.95
2000	21.72
2001	22.71
2002	23.89
2003	25.04
2004	26.19
2005	27.32
2006	28.35
2007	29.41
2008	30.41
2009	31.37
2010	32.6
2011	33.62
2012	34.94
2013	36.31
2014	37.8
2015	39.5
2016	41.33