Year	% of total
1970	23.965077188414636
1971	23.93572443503208
1972	22.830714543158454
1973	22.325443090464024
1974	23.930428517729606
1975	22.958872021146387
1976	23.326412732027986
1977	24.039990662372464
1978	23.730062423207286
1979	22.299360788183794
1980	22.054984841677495
1981	22.580895287431012
1982	26.106371047049358
1983	30.46514458486226
1984	32.91048477268352
1985	34.53340394548449
1986	35.062989712366154
1987	35.10652099621148
1988	36.79431133410741
1989	37.22967818539142