Year	Number
1992	20.46535
1993	20.0981
1994	19.58642
1995	19.76087
1998	19.26959
1999	19.53285
2000	18.2068
2001	17.43863
2002	16.66112
2003	15.93862
2004	15.44266
2005	16.03553
2006	16.02405
2007	15.96701
2008	15.32719
2009	15.14091
2010	14.96616
2011	14.96367
2012	14.90909
2013	15.36216
2014	16.47603
2015	17.57007
2016	18.33759
2017	18.80255
2018	19.23259