Year	% of total
1970	39.76977367629864
1971	39.37933675212463
1972	35.30966153269387
1973	36.5222950942108
1974	33.814076620845306
1975	35.950071407825874
1976	35.305405029369844
1977	35.490914602212406
1978	35.410922306870916
1979	36.53213539039187
1980	35.91936036566812
1981	35.70174535837714
1982	34.7984136370444
1983	33.95794986111487
1984	23.318718368416537
1985	30.085554236345242
1986	31.611494572628335
1987	30.750045089176893
1988	30.380528906383113
1989	28.76543964952984
1990	28.822035854427945
1991	28.96704302715899
1992	28.647904557968793
1993	27.436571782178216
1994	22.845461978740804
1995	23.182917002417405
1996	22.158905893845652
1997	20.904422726519794
1998	19.42286348501665
1999	17.937701396348015
2000	16.936534524474222
2001	16.235701240026916
2002	15.807526460211681
2003	14.980343471963584
2004	15.35368901445181
2005	14.096413068311628
2006	13.721264367816092
2007	13.757674476882595
2008	14.163548904329234