Year	% net
1971	50.12019
1972	49.32399
1973	55.80814
1975	59.79752
1976	63.38247
1977	65.86687
1978	66.82714
1979	69.39231
1980	72.44047
1981	73.15491
1999	85.90927
2000	87.17315
2001	88.5063
2002	88.9374
2003	89.2517
2004	90.14459
2005	91.53281
2006	91.14519
2007	90.42804
2008	89.86562
2009	89.45742
2010	89.61511
2011	88.57775
2012	89.14063
2013	89.97197
2014	90.9262
2015	92.28014
2016	94.27312
2017	96.05046