Year	% of total
1970	71.57026550525515
1971	73.98631913278462
1972	80.86775493318649
1973	84.69938302468543
1974	81.76611998730381
1975	79.2207237544525
1976	82.81426465096284
1977	82.78925138196833
1978	83.23761550287202
1979	81.9129046935763
1980	79.79401532100869
1981	77.06362504433692
1982	75.2605867553041
1983	76.68390771191518
1984	78.25947509270557
1985	80.848123541363
1986	80.49848526007038
1987	79.90632192112423
1988	79.68867479466081
1989	80.11608346193077
1990	59.35659265971908
1991	59.53887884267631
1992	58.74001774622892
1993	58.249452954048145
1994	58.42794759825327
1995	60.070120763537204
1996	61.37082601054481
1997	62.5
1998	62.99005266237566
1999	63.44549125168237
2000	64.12825651302605
2001	64.98559077809799
2002	66.05653382761817
2003	66.57777777777778
2004	66.98656429942419
2005	67.61983131042996
2006	66.79035250463822
2007	66.01901612236462
2008	65.48783024755565