Year	% of total
1970	86.2355428036602
1971	83.27648631488195
1972	83.83366263488699
1973	84.90204816390948
1974	84.11721526337959
1975	84.43128101482141
1976	84.20180791721064
1977	85.35504082379516
1978	85.76731312067628
1979	86.43363229712634
1980	86.02935284628973
1981	85.84661759645336
1982	86.1325184409626
1983	86.21996114393322
1984	85.68735639461552
1985	85.54864190732253
1986	85.45880735823121
1987	86.49713495935724
1988	84.03511807469515
1989	84.34301650960879
1990	75.64102564102564
1991	77.24550898203593
1992	77.84431137724552
1993	78.23529411764706
1994	72.99270072992701
1995	75.64102564102564
1996	76.64670658682635
1997	76.33136094674556
1998	76.70454545454545
1999	75.86206896551724
2000	76.50273224043715
2001	73.37278106508876
2002	76.5
2003	77.25118483412322
2004	76.38888888888889
2005	76.36363636363637
2006	77.82426778242679
2007	79.45736434108527
2008	81.42857142857143