Year	% of total
1970	63.43439328111782
1971	64.69067433719891
1972	65.82110202242994
1973	64.93896188437685
1974	62.46117642075617
1975	59.64884096209002
1976	55.76270573956612
1977	56.95939342154072
1978	57.14142871848531
1979	56.79863641223864
1980	63.326403375308125
1981	64.43739332051032
1982	61.54003470053113
1983	64.10350920037547
1984	62.614324062522066
1985	62.25720968354702
1986	60.987924251290806
1987	60.773813376764
1988	60.415624094472854
1989	60.1945429411991
1990	58.434782608695656
1991	57.815126050420176
1992	58.25396825396826
1993	58.734939759036145
1994	56.86274509803921
1995	55.851851851851855
1996	53.80200860832137
1997	52.55172413793103
1998	50.86782376502003
1999	50.442477876106196
2000	49.20245398773006
2001	49.524940617577194
2002	49.82698961937716
2003	48.07467911318553
2004	47.88087056128293
2005	48.9010989010989
2006	48.580786026200876
2007	50.156412930135566
2008	50.8646998982706