Year	% of total
1970	33.747004453096835
1971	33.67970536909356
1972	32.920877665149156
1973	32.89911763772533
1974	32.60852593390304
1975	33.78366432345337
1976	33.45295690275251
1977	32.875115495120006
1978	32.67394186911246
1979	31.719920447893514
1980	31.461850854897527
1981	30.91880955939136
1982	31.03523448432442
1983	30.603784693165885
1984	31.954889010116688
1985	30.742516081613854
1986	30.229213930527248
1987	28.999577073810066
1988	27.643814550225564
1989	26.466487883280703
1990	40.647482014388494
1991	39.03030303030303
1992	38.2640586797066
1993	37.91411042944785
1994	37.88819875776397
1995	37.212276214833764
1996	37.532467532467535
1997	38.30911492734479
1998	38.76712328767123
1999	38.59154929577465
2000	39.49704142011834
2001	39.87823439878234
2002	41.33545310015898
2003	42.45439469320066
2004	42.90657439446367
2005	44.626593806921676
2006	44.04332129963899
2007	44.40298507462687
2008	45.124282982791584