Year	% net
1977	15.07491
1978	15.69529
1979	16.48618
1980	17.79398
1981	17.64125
1982	18.37156
1983	19.17218
1984	19.38607
1985	19.05681
1986	18.79522
1987	18.8602
1988	18.87937
1989	18.76682
1990	18.3054
1991	19.30821
1992	20.03638
1993	20.69675
1994	21.65398
1995	22.73375
1996	23.32271
1997	23.71586
1998	24.54441
1999	25.16874
2000	25.98398
2001	26.73604
2002	27.77557
2003	28.20845
2004	28.93527
2005	29.26584
2006	30.56446
2007	31.48136
2008	32.34586
2009	33.53541
2010	34.35531
2011	34.67116
2012	35.75626
2013	36.73111
2014	37.50083
2015	38.44527
2016	39.29096
2017	38.94056
2018	40.25338