Year	% of total
1970	66.27552728328514
1971	63.64824928727375
1972	63.65567573401535
1973	60.20185760670563
1974	60.23589627846372
1975	59.933652992478805
1976	60.65693479068841
1977	62.433287639509075
1978	62.783517184481184
1979	62.78371010658659
1980	60.65251393433794
1981	57.97816915741604
1982	54.43289055291752
1983	52.96335792049213
1984	52.888108858724515
1985	53.92308416724748
1986	56.38449681641834
1987	56.97744050521988
1988	59.04191548296032
1989	59.41354688090814
1990	56.03448275862068
1991	55.71030640668524
1992	54.891304347826086
1993	52.732240437158474
1994	52.879581151832454
1995	49.18032786885246
1996	51.76767676767676
1997	48.95833333333333
1998	45.96774193548387
1999	47.179487179487175
2000	44.76439790575916
2001	47.688564476885645
2002	48.717948717948715
2003	47.16981132075472
2004	46.74418604651163
2005	46.31336405529954
2006	47.19101123595505
2007	48.026315789473685
2008	48.268398268398265