Year	% of total
1970	36.9381921263726
1971	37.58830261696607
1972	38.63960533748426
1973	40.06812663122805
1974	40.73862689324524
1975	40.26427053017873
1976	39.622177482108896
1977	38.98442756604999
1978	40.505834821467616
1979	39.94466469235709
1980	41.46936067233254
1981	41.922443008148456
1982	42.17722915708646
1983	42.13341505087615
1984	42.563839387423904
1985	42.272575598267686
1986	42.44575104946198
1987	42.99274897221746
1988	43.60901980830751
1989	45.69937671681829
1990	32.38493723849372
1991	33.050468959356856
1992	31.60919540229885
1993	28.973843058350102
1994	26.76659528907923
1995	26.019845644983462
1996	25.612472160356347
1997	24.715261958997722
1998	23.973825104104698
1999	24.73253618628068
2000	24.766977363515313
2001	25.016949152542374
2002	24.735729386892178
2003	24.113475177304963
2004	23.976608187134502
2005	22.77580071174377
2006	21.988795518207283
2007	22.84887924801157
2008	22.48563218390805