Year	% net
1970	39.53289
1971	39.09801
1972	42.00424
1973	45.20219
1974	45.0693
1975	47.34674
1976	49.15795
1977	50.16169
1978	51.2896
1979	52.11719
1980	53.42768
1981	54.13523
1982	53.38477
1983	53.7774
1984	53.4829
1985	52.81649
1986	52.85209
1987	52.36676
1988	54.42953
1989	54.02915
1990	53.21362
1991	54.43862
1992	54.26492
1993	54.24413
1994	54.9774
1995	56.22271
1996	56.44241
1997	58.3462
1998	58.43349
1999	58.14256
2000	60.42693
2001	62.51889
2002	65.64719
2003	68.59243
2004	70.95124
2005	73.39791
2006	75.55129
2007	76.9554
2008	79.26928
2009	79.44566
2010	79.00299
2011	79.98977
2012	80.57588
2013	81.27714
2014	81.56356
2015	81.13239
2016	81.11583
2017	80.98355
2018	80.77344