Year	Number
1994	20.22001
1995	20.24173
1996	20.23127
1997	20.29017
1998	20.5116
1999	20.65233
2000	20.37901
2001	20.02027
2002	19.88522
2003	19.10401
2004	18.31414
2005	17.86489
2006	17.67359
2007	17.46481
2008	17.38244
2009	17.01977
2010	16.6572
2011	16.42645
2012	16.42589
2013	15.97704
2014	16.03913
2015	16.50545
2016	17.00307
2017	16.74694
2018	16.56002