Year	% net
1971	98.18254
1972	97.3134
1973	96.35756
1974	95.86765
1975	95.78484
1976	95.87591
1977	96.19219
1978	96.26426
1979	96.43068
1980	97.7863
1981	97.65796
1982	96.70084
1983	95.11314
1984	94.64484
1985	93.57046
1986	95.18731
1987	98.01106
1988	99.67916
1989	99.71212
1990	99.78913
1991	98.18471
1992	96.65488
1998	99.908
1999	99.94032
2000	99.94481
2001	99.93639
2002	99.82263
2003	99.90834
2004	98.13312
2005	98.78009
2006	98.42751
2007	96.53232
2008	98.63343
2009	97.88299
2010	98.01015
2011	98.11699
2012	98.35876
2013	99.72456
2014	99.89948
2015	99.93433
2016	99.65208
2017	99.49182