Year	% net
1970	67.69739
1971	67.66358
1972	68.79651
1973	71.46394
1974	72.45171
1975	73.82114
1976	74.54764
1977	74.58767
1978	73.40278
1979	73.81362
1980	74.76424
1981	75.78939
1982	76.25739
1983	76.69156
1984	77.08635
1985	77.84499
1986	78.6484
1987	78.89348
1988	79.60115
1989	80.3487
1990	79.99815
1991	80.37664
1992	80.20457
1993	80.31069
1994	80.36157
1995	79.92776
1996	79.64717
1997	79.77497
1998	80.30519
1999	81.11155
2000	81.80105
2001	82.05026
2002	82.34478
2003	83.78825
2004	85.04631
2005	85.72567
2006	86.16867
2007	87.51534
2008	87.72813
2009	87.75058
2010	87.78454
2011	87.83409
2012	88.20426
2013	88.21766
2014	88.45404
2015	88.34511
2016	88.5774
2017	88.43887
2018	88.60731