Year	% of total
1970	24.092214358578975
1971	23.461060050222564
1972	23.399921226546596
1973	23.66807150447255
1974	23.969737400979348
1975	24.2726924629096
1976	25.054047592924107
1977	25.171632883707918
1978	24.250108371094058
1979	23.154751839466368
1980	25.26355064755514
1981	26.05759472376455
1982	24.89454254400044
1983	23.532893417429673
1984	23.45679397598007
1985	24.22949935372849
1986	24.428353037651295
1987	24.90071451445817
1988	24.167096931679023
1989	23.8583181417964
1990	22.11449676823638
1991	23.19047619047619
1992	23.568702290076335
1993	23.936932632584806
1994	24.133016627078383
1995	24.548049476688867
1996	26.712666338097584
1997	27.71553823672674
1998	28.259838786154575
1999	27.8125
2000	30.49812030075188
2001	30.73308270676692
2002	29.868361325465276
2003	28.59611231101512
2004	27.351129363449694
2005	28.104026845637588
2006	29.56081081081081
2007	21.075455333911535
2008	21.51360544217687