Year	% of total
1970	7.776890918223844
1971	11.73304677582668
1972	11.118552570368399
1973	10.65140490640151
1974	11.548599249013039
1975	10.247842284388941
1976	10.76143340873584
1977	9.92213201468771
1978	9.568880329915693
1979	7.976107664707639
1980	9.096573950427691
1981	9.910037218932414
1982	9.198140866927485
1983	9.426816802899555
1984	11.44041836787238
1985	11.421696254245653
1986	11.596850317682962
1987	9.477322099246138
1988	11.666312443730998
1989	10.887812965739704
1990	21.245136186770427
1991	21.109817617384554
1992	21.12236944660951
1993	20.809248554913296
1994	20.645905420991927
1995	19.096728307254622
1996	20.208023774145616
1997	20.54538662682107
1998	19.173838209982787
1999	18.977119784656796
2000	20.028060329708875
2001	21.34453781512605
2002	21.384803921568626
2003	21.42254709024459
2004	23.26760563380282
2005	23.656200106439595
2006	25.87374695204552
2007	26.437079233557743
2008	26.58196921573418