Year	Number of
1990	28.51
1991	28.42
1992	27.81
1993	27.71
1994	27.5
1995	26.63
1996	26.17
1997	25.42
1998	24.44
1999	23.52
2000	23.59
2001	21.81
2002	21.35
2003	20.63
2004	20.47
2005	20.45
2006	20.46
2007	19.65
2008	19.6
2009	19.59
2010	19.71
2011	19.51
2012	19.72
2013	20.1
2014	20.9
2015	21.64
2016	22.31