Year	% of total
1970	22.23538296193102
1971	20.488085142259553
1972	20.30815693443671
1973	20.800080577565762
1974	20.124299868424238
1975	19.91675408048743
1976	20.119520323444466
1977	19.912555583971844
1978	20.201517929067403
1979	20.255500308985923
1980	20.47248303371471
1981	21.105958302777715
1982	21.71394694265999
1983	21.310799298244856
1984	21.67971425536023
1985	21.812262579388385
1986	21.651972989606342
1987	20.948074941092713
1988	22.981272370929577
1989	21.948013046484892
1990	10.198789974070872
1991	9.296264118158124
1992	9.275618374558304
1993	9.008189262966333
1994	7.7285579641847315
1995	8.399209486166008
1996	8.291203235591507
1997	7.924921793534932
1998	8.055853920515576
1999	8.178844056706652
2000	8.277404921700224
2001	8.636363636363637
2002	8.400460299194476
2003	8.440797186400937
2004	8.056872037914692
2005	7.7764277035236935
2006	8.064516129032258
2007	7.994923857868021
2008	7.958921694480104