Year	Number of
1990	18.23
1991	18.32
1992	18.48
1993	18.68
1994	18.89
1995	19.11
1996	19.16
1997	19.21
1998	19.27
1999	19.32
2000	19.36
2001	20.23
2002	21.14
2003	22.12
2004	23.22
2005	24.49
2006	25.86
2007	27.37
2008	29.05
2009	30.84
2010	32.74
2011	34.37
2012	36.08
2013	37.85
2014	39.67
2015	41.54
2016	43.56