Year	% of total
1970	36.862149638654515
1971	36.99127146023188
1972	36.64870581617454
1973	36.38923846130201
1974	37.278008397291366
1975	36.842176224992926
1976	37.69658612193856
1977	37.19618440068281
1978	37.57071281467491
1979	37.09366756287445
1980	37.14612677531075
1981	36.85342640570297
1982	36.314260616900754
1983	45.443230910409774
1984	17.536533907005133
1985	17.63974384725724
1986	18.031005744568336
1987	16.34227347352358
1988	13.426333904301824
1989	12.12384902179446