Year	% of total
1970	24.060580195870646
1971	21.6714461291964
1972	19.64450018351392
1973	18.723347253237236
1974	16.67930699149586
1975	15.137061643729849
1976	15.495805307801577
1977	15.587489466635304
1978	13.837497923037088
1979	13.617023649897522
1980	14.115238544458522
1981	14.617032918414791
1982	14.515660629095843
1983	13.862266256857856
1984	13.816704193334164
1985	13.594507386470973
1986	13.427477628030902
1987	12.179037616225555
1988	11.475673312394749
1989	10.997172728530842
1990	16.723910171730516
1991	15.653577192038732
1992	14.405179390342596
1993	12.945693911135493
1994	11.863938053097344
1995	11.524163568773234
1996	11.077933711555689
1997	10.748091603053435
1998	10.485933503836318
1999	10.507482108002602
2000	10.391766268260293
2001	9.802563214409421
2002	8.553100498930863
2003	8.705114254624592
2004	9.24645067346196
2005	9.734513274336283
2006	10.172026925953627
2007	10.538286580742987
2008	10.571317528177225