Year	% of total
1970	30.978307061836862
1971	30.57055631039506
1972	30.659496094426448
1973	20.245526568076933
1974	20.14206952009812
1975	18.76688986435848
1976	18.04795439007563
1977	13.692381648302868
1978	15.724081006955515
1979	16.004110532371886
1980	17.07124271077865
1981	18.858254482393487
1982	18.866474520117116
1983	17.91813901188575
1984	16.8104024786999
1985	16.4779939545435
1986	16.235553205410234
1987	16.12786024389478
1988	15.867967041276817
1989	15.728384570500955