Year	% of total
1970	4.192001906376636
1971	4.068683001382351
1972	3.994384450930197
1973	3.945856119263343
1974	3.832084815062211
1975	3.758781002330331
1976	4.638144030198885
1977	4.568277566094285
1978	7.665172964946643
1979	8.27208385792847
1980	8.358016421382512
1981	8.843197885832051
1982	9.061554052726498
1983	8.782813018766607
1984	9.2405857077657
1985	9.911775308990284
1986	7.862876321160786
1987	9.62493616690045
1988	9.98187132929531
1989	10.70426776601245