Year	Number of
1990	18.25
1991	18.63
1992	19.02
1993	19.41
1994	19.83
1995	20.3
1996	20.61
1997	20.97
1998	21.37
1999	21.8
2000	22.27
2001	22.79
2002	23.36
2003	23.96
2004	24.61
2005	25.34
2006	26.01
2007	26.73
2008	27.51
2009	28.37
2010	29.33
2011	30.27
2012	31.3
2013	32.38
2014	33.56
2015	34.83
2016	36.17