Year	% net
1970	52.79379
1971	52.27325
1972	54.0825
1973	56.84676
1974	56.51517
1975	58.43089
1976	59.33974
1977	61.32207
1978	60.31376
1979	60.64285
1980	62.33837
1981	64.07619
1982	65.6872
1983	67.0765
1984	68.30123
1985	68.63692
1986	69.67261
1987	69.21027
1988	70.74882
1989	72.81098
1990	72.09403
1991	72.78815
1992	73.09987
1993	73.91847
1994	74.91612
1995	74.56866
1996	75.31573
1997	75.13803
1998	74.92386
1999	75.52477
2000	76.91052
2001	77.6674
2002	78.36447
2003	82.10792
2004	83.4887
2005	84.82799
2006	86.02039
2007	87.83729
2008	88.43094
2009	89.01977
2010	89.42242
2011	89.52529
2012	89.6106
2013	89.84268
2014	89.8341
2015	89.64035
2016	89.77317
2017	89.72967
2018	89.59618