Year	% net
1971	35.33232
1972	39.14199
1973	42.07355
1974	45.56385
1975	49.32935
1976	53.29621
1977	56.98226
1978	60.16836
1979	63.7847
1980	68.64021
1981	72.88877
1984	80.49847
1985	82.37735
1986	84.68302
1989	84.63785
1991	88.06848
1992	86.85311
1996	95.93705
1997	94.28475
1998	93.84005
1999	93.26666
2000	92.63574
2001	92.98384
2002	92.85815
2003	93.75619
2004	94.51301
2005	95.19021
2006	94.37853
2007	94.14674
2008	93.38299
2009	94.64991
2010	94.90295
2011	95.63541
2012	96.42506
2013	97.76121
2014	98.16688
2015	97.70791
2016	98.14563
2017	98.00711