Year	% of total
1970	20.13799109143501
1971	20.125113262677786
1972	19.93065714895455
1973	20.671734399961892
1974	20.56786899756583
1975	20.525503392093476
1976	22.737635961404738
1977	21.628009751399034
1978	24.576967463217027
1979	25.251161686974744
1980	24.72545343672912
1981	24.675953650972406
1982	24.414304252827762
1983	24.847029744830493
1984	24.86035023402975
1985	23.743812901191216
1986	23.138251036100733
1987	23.378659773114833
1988	20.39168106229904
1989	19.909809871236796