Year	% net
1971	28.1823
1972	31.73813
1973	34.75801
1974	37.99383
1975	41.53676
1976	45.36355
1977	49.26265
1978	52.84017
1979	57.00365
1980	63.48912
1981	68.84013
1984	77.892
1985	80.52252
1986	83.35642
1989	84.43763
1991	86.89837
1992	86.1317
1996	95.90705
1997	94.12812
1998	93.74754
1999	93.16661
2000	92.98875
2001	93.83554
2002	93.80144
2003	94.84258
2004	95.74507
2005	96.33713
2006	94.97802
2007	94.34829
2008	93.45759
2009	94.5104
2010	94.7059
2011	95.40711
2012	96.28801
2013	97.59765
2014	98.09038
2015	97.47823
2016	97.87641
2017	97.80743