Year	Number of
1990	17.99
1991	16.85
1992	16.12
1993	16.83
1994	16.54
1995	16.34
1996	16.99
1997	16.94
1998	17.14
1999	17.31
2000	17.41
2001	17.33
2002	17.32
2003	17.82
2004	19
2005	20.32
2006	20.52
2007	20.67
2008	21.09
2009	20.89
2010	20.71
2011	20.86
2012	21.54
2013	22.15
2014	22.94
2015	24.13
2016	25.99