Year	% net
1970	93.61511
1971	94.01978
1972	94.43481
1973	94.771
1974	95.08514
1975	93.31517
1976	92.02867
1977	93.91365
1978	94.03244
1979	93.99425
1980	92.85679
1981	93.53299
1982	94.5126
1983	95.20437
1984	95.0615
1985	94.69073
1986	94.44768
1987	95.46006
1988	95.29849
1989	96.68515
1990	95.42339
1991	93.44562
1992	92.338
1993	91.46254
1994	91.70484
1995	91.99979
1996	92.13167
1997	92.47161
1998	92.92004
2000	92.41532
2001	91.77903
2004	91.43604
2005	90.86625
2007	90.88696
2015	90.79281
2016	89.15522
2017	88.25528
2018	87.76584