Year	% net
1970	28.28805
1971	26.36815
1972	29.51175
1973	33.48462
1974	33.07053
1975	35.99184
1976	37.89326
1977	40.15255
1978	41.48553
1979	42.82067
1980	44.70796
1981	45.95404
1982	44.92837
1983	45.02923
1984	45.62408
1985	44.9395
1986	45.19357
1987	44.76783
1988	47.67229
1989	47.60985
1990	47.03165
1991	48.6695
1992	48.91322
1993	49.12683
1994	50.05767
1995	51.2818
1996	51.52341
1997	53.62724
1998	53.92714
1999	54.11293
2000	56.53984
2001	58.72146
2002	62.19595
2003	65.23874
2007	74.4765
2008	76.57559
2009	77.27672
2010	76.9684
2011	77.85486
2014	79.72205
2015	79.15789
2016	79.11963
2017	78.69473
2018	78.44513