Year	% net
1981	78.95831
1982	79.28325
1983	79.61639
1984	79.89069
1985	80.47146
1986	81.36614
1987	81.791
1988	81.94486
1989	81.95734
1990	81.78736
1991	81.56318
1996	83.55694
1997	83.4842
1998	83.0164
1999	83.461
2000	84.63935
2001	85.8942
2002	86.27247
2003	86.65042
2004	85.97591
2005	85.80879
2006	86.20452
2007	86.4081
2008	86.72783
2009	86.6353
2010	87.83752
2011	88.24032
2012	88.28786
2013	89.4201
2014	89.92729
2015	90.22944
2016	89.93778
2017	90.20232
2018	89.92563