Year	% of total
1970	30.8216375767833
1971	32.37159190725989
1972	32.10024265890298
1973	32.25960564929527
1974	33.441514717622205
1975	33.68067398029474
1976	32.76500731404147
1977	32.58981000950196
1978	32.34578130879196
1979	30.7929909037998
1980	31.363966837949732
1981	32.12680901132562
1982	31.890102848219858
1983	31.715210513144353
1984	30.94431516194312
1985	30.41165166380851
1986	29.7194782664157
1987	28.833542421452403
1988	28.359206824425815
1989	27.74893379219843
1990	25.694344791598724
1991	25.750175365669897
1992	26.141256976335747
1993	26.789801458455315
1994	27.15419501133787
1995	27.71774107047088
1996	27.908204711616573
1997	28.40363570964127
1998	28.938234373666393
1999	29.418601272626898
2000	29.442275104987843
2001	29.60440214158239
2002	30.089273534716643
2003	29.95587365611779
2004	30.186200681259262
2005	30.542951744435587
2006	30.572312214839087
2007	31.021134938453198
2008	30.644818692155972