Year	Number of
1990	15.82
1991	16.24
1992	16.64
1993	17.06
1994	17.56
1995	17.89
1996	18.45
1997	19.48
1998	20.2
1999	21.3
2000	21.46
2001	22.31
2002	23.22
2003	24.12
2004	25
2005	25.98
2006	27.05
2007	28.28
2008	29.17
2009	29.99
2010	30.62
2011	31.33
2012	31.98
2013	32.65
2014	33.32
2015	33.98
2016	34.36