Year	Number of
1990	15.13
1991	15.73
1992	16.43
1993	17.3
1994	18.33
1995	19.55
1996	20.44
1997	21.2
1998	22
1999	22.86
2000	24
2001	24.97
2002	26.16
2003	27.65
2004	29.16
2005	30.62
2006	31.51
2007	32.26
2008	33.15
2009	34.08
2010	35.09
2011	34.58
2012	33.61
2013	33.17
2014	32.68
2015	32.5
2016	32.49