Year	Number
1980	8.3850106308
1981	8.7132352941
1982	9.0414599575
1983	9.3696846208
1984	9.6979092842
1985	10.0261339476
1986	10.3028880227
1987	10.5796420978
1988	10.8563961729
1989	11.1331502481
1990	11.4099043232
1991	11.8594082211
1992	12.3089121191
1993	12.758416017
1994	13.207919915
1995	13.6574238129
1996	14.1069277108
1997	14.5564316088
1998	15.0059355067
1999	15.4554394047
2000	15.9049433026
2001	16.3574592488
2002	16.8099751949
2003	17.223733168
2004	17.6762491141
2005	18.1303153792
2006	18.1303153792
2007	18.1303153792
2008	18.1303153792
2009	18.1303153792
2010	18.1303153792
2011	18.1303153792
2012	18.1303153792
2013	18.1303153792
2014	18.1303153792
2015	18.1303153792
2016	18.1303153792
2017	18.1303153792
2018	18.1303153792
2019	18.1303153792
2020	18.1303153792