Year	% of total
1970	44.508050065467394
1971	42.76142327735738
1972	40.47676179337726
1973	38.300492354938
1974	36.202955983724635
1975	36.24112695310103
1976	35.974667111545
1977	35.86245749530264
1978	35.67025019876949
1979	34.977882124609586
1980	35.70901296869074
1981	39.75325202332869
1982	37.491794257267266
1983	34.41990878252763
1984	34.90296283191531
1985	36.72380462650051
1986	35.29224181316068
1987	32.45652891603191
1988	31.417302043582012
1989	31.136986561048204