Year	% net
1970	93.52401
1971	93.9191
1972	94.3791
1973	94.51658
1974	95.13201
1975	92.96009
1976	91.58968
1977	93.55262
1978	93.50518
1979	93.45815
1980	92.08362
1981	92.70178
1982	94.01698
1983	94.43814
1984	94.15696
1985	94.01058
1986	93.84913
1987	95.482
1988	95.03937
1989	96.43917
1990	94.69399
1991	92.8974
1992	92.68964
1993	91.97852
1994	92.13779
1995	92.3927
1996	92.43389
1997	92.40152
1998	92.58138
1999	92.32086
2000	92.3124
2001	91.62593
2004	91.30068
2005	90.7363
2007	90.60624
2008	91.04258
2010	90.52427
2011	90.59603
2012	90.24916
2013	89.6081
2014	89.39119
2015	89.64632
2016	89.18064
2017	88.34162
2018	87.89515