Year	% net
1974	39.33776
1975	41.41874
1976	42.55757
1977	43.14823
1978	43.57612
1979	44.00972
1980	44.58664
1981	43.72112
1982	43.71771
1983	43.90189
1984	43.76515
1985	44.05335
1986	44.13203
1987	43.9783
1988	44.12591
1989	43.91085
1990	44.91721
1991	46.09923
1992	46.60364
1993	46.93467
1994	47.50834
1995	48.41054
1996	49.31546
1997	50.0751
1998	49.59936
1999	49.9941
2000	50.51674
2001	51.16664
2002	52.52891
2003	53.1705
2004	54.72588
2005	55.48825
2006	55.72598
2007	56.05392
2008	56.32618
2009	57.11752
2010	57.58918
2011	57.55182
2012	57.77065
2013	57.79338
2014	58.16581
2015	58.15793
2016	58.49717
2017	58.7646