Year	% net
1974	37.5399
1975	39.33065
1976	40.44336
1977	41.39258
1978	41.71591
1979	41.97845
1980	42.36287
1981	41.70864
1982	41.92359
1983	42.23945
1984	42.18352
1985	42.5041
1986	42.35105
1987	42.24385
1988	42.40208
1989	42.26781
1990	43.33144
1991	44.3331
1992	44.90532
1993	45.37381
1994	45.88951
1995	46.71128
1996	47.62519
1997	48.51701
1998	48.37105
1999	48.87922
2000	49.39854
2001	50.45241
2002	51.64261
2003	52.38358
2004	54.22056
2005	54.81673
2006	54.88348
2007	55.64314
2008	55.85496
2009	56.29246
2010	56.604
2011	56.60552
2012	56.96321
2013	56.94212
2014	57.25112
2015	57.07453
2016	57.3006
2017	57.54649