Year	% of total
1970	38.40716624242802
1971	33.85740031642497
1972	29.86676999594986
1973	29.00488159450872
1974	24.283910306527993
1975	29.738788590545738
1976	27.872550363023052
1977	32.054803604369006
1978	32.409081776103044
1979	27.136532699692197
1980	31.837539967895857
1981	36.72235548410032
1982	39.79625227077534
1983	39.804497543452705
1984	38.577282299311804
1985	37.77946935772919
1986	37.77991889747307
1987	39.07381837908606
1988	37.22250813230002
1989	37.36734683061636
1990	20.01236967662131
1991	20.883603853832135
1992	20.951068228807717
1993	21.206175893542607
1994	21.651991614255763
1995	23.640724946695098
1996	25.59857837635615
1997	28.298372868065087
1998	31.18168694576201
1999	33.85576501534415
2000	36.7865932262979
2001	35.566659096070865
2002	34.693429856312385
2003	34.219689775245335
2004	33.78735515348648
2005	33.9040762720109
2006	33.96880415944541
2007	33.522181678509696
2008	33.20267686424474