Year	% of total
1970	49.77604566653678
1971	50.51815404201145
1972	49.430847223432465
1973	48.43358566329565
1974	47.93115960971888
1975	51.35404016573717
1976	49.33396700682153
1977	49.14139280064418
1978	50.76537564184699
1979	50.82570769855204
1980	50.12417769227363
1981	53.2246209239525
1982	53.02861280982124
1983	52.91017084519758
1984	53.95210344785506
1985	55.15296414165096
1986	53.45874309062888
1987	54.694266857138686
1988	54.704845836504475
1989	55.22792730234097
1990	71.71270718232044
1991	72.93754818812644
1992	67.77358490566037
1993	66.6157372039725
1994	66.1512027491409
1995	62.78674596431606
1996	61.23833757421544
1997	64.34245366284202
1998	66.95652173913044
1999	65.39649845520083
2000	59.04761904761905
2001	64.74609375
2002	65.26429341963322
2003	62.24696356275303
2004	63.13405797101449
2005	63.46328195829556
2006	65.66566566566566
2007	62.412761714855435
2008	75.49450549450549