Year	% net
1974	38.42698
1975	40.36303
1976	41.49028
1977	42.26168
1978	42.63487
1979	42.98046
1980	43.45953
1981	42.70252
1982	42.8085
1983	43.05986
1984	42.96536
1985	43.27153
1986	43.23375
1987	43.10306
1988	43.2567
1989	43.08395
1990	44.1201
1991	45.20597
1992	45.74329
1993	46.14183
1994	46.68408
1995	47.5443
1996	48.4549
1997	49.28442
1998	48.97634
1999	49.42849
2000	49.94965
2001	50.80277
2002	52.07714
2003	52.76738
2004	54.46747
2005	55.1457
2006	55.29746
2007	55.84291
2008	56.08131
2009	56.69121
2010	57.08271
2011	57.06738
2012	57.3443
2013	57.34041
2014	57.68301
2015	57.59482
2016	57.88084
2017	58.13102