Year	% of total
1970	40.41016091009367
1971	38.74626123644019
1972	38.5459454243636
1973	38.68499993571167
1974	39.23506494343192
1975	38.929521456339586
1976	37.89870313918461
1977	37.7519920046438
1978	39.14945298720363
1979	39.26988042069861
1980	40.40004873435788
1981	40.75988105595887
1982	41.92580011382551
1983	41.96973931606088
1984	41.35290623224469
1985	40.36850066266863
1986	39.57532717809359
1987	39.301209432917545
1988	39.06995416576398
1989	37.63956198983466
1990	45.70977917981073
1991	45.63046192259675
1992	45.69074778200253
1993	45.674628792769525
1994	46.01652892561984
1995	46.810664866689166
1996	46.84373922042083
1997	47.76607337450054
1998	48.100789770590445
1999	50.19607843137255
2000	50.73770491803279
2001	51.85185185185185
2002	51.71957671957672
2003	52.46800731261426
2004	53.41121495327103
2005	57.17834078489816
2006	58.107416879795394
2007	58.540293968575774
2008	59.385834571570086