Year	% net
1977	33.90233
1978	33.76977
1979	33.65174
1980	33.30242
1981	33.33715
1982	33.75873
1983	34.06513
1984	34.21336
1985	34.45581
1986	34.46101
1987	34.05449
1988	33.93187
1989	34.18079
1990	35.48146
1991	36.50426
1992	37.22925
1993	38.22753
1994	38.44236
1995	39.13766
1996	39.83557
1997	40.80905
1998	41.33378
1999	41.6973
2000	43.11731
2001	44.14688
2002	45.65417
2003	46.74431
2004	48.56321
2005	49.59153
2006	49.52109
2007	50.86511
2008	50.99981
2009	51.49106
2010	51.78348
2011	51.77325
2012	52.77837
2013	53.08489
2014	53.43726
2015	53.47785
2016	53.62416
2017	53.98616