Year	Number of
1990	19.38
1991	20.27
1992	20.92
1993	21.5
1994	22.5
1995	23.59
1996	24.85
1997	25.21
1998	25.97
1999	25.91
2000	26.06
2001	25.78
2002	25.26
2003	24.74
2004	24.08
2005	23.67
2006	23.52
2007	23.63
2008	23.96
2009	24.35
2010	24.82
2011	25.36
2012	25.93
2013	26.53
2014	27.12
2015	27.45
2016	27.98