Year	% of total
1970	60.859014015259916
1971	67.89231896202304
1972	64.59713901568972
1973	68.04933328306039
1974	66.90145229341431
1975	64.86558327029566
1976	64.67922467886939
1977	69.48169725845382
1978	65.88613026326239
1979	64.63659264244284
1980	64.7418204073274
1981	66.90407430055085
1982	66.20071942469849
1983	64.99125696678132
1984	68.2454028942534
1985	66.66094011030532
1986	66.44145086815418
1987	64.15604625782935
1988	66.59359437726002
1989	66.52839019291005
1990	84.88641144299537
1991	83.3727554385848
1992	83.55003940110322
1993	83.34042622843486
1994	83.38475382439903
1995	84.76649012999519
1996	82.63081872496882
1997	82.42139780106731
1998	82.36939712076445
1999	81.70867653434074
2000	82.523734906443
2001	81.52806894945259
2002	81.65528302408539
2003	81.49854381784485
2004	81.74117528067158
2005	82.66133091714487
2006	81.99312714776632
2007	81.65314891561364
2008	81.35155850792029