Year	% of total
1970	28.668359807544764
1971	28.058213411448403
1972	31.80869145846397
1973	30.061313791773863
1974	29.3726379137719
1975	29.34385832162053
1976	30.821934768115383
1977	31.873838547031454
1978	29.4322620634962
1979	30.58282091498823
1980	30.07262548459052
1981	25.587121571456038
1982	31.845834988676675
1983	28.504975790663355
1984	23.753517067028948
1985	23.65143473972392
1986	27.469815416179404
1987	30.085182537803647
1988	22.06248119561174
1989	22.54538917857906
1990	18.654434250764528
1991	14.319248826291082
1992	12.121212121212121
1993	10.776545166402537
1994	9.686221009549795
1995	8.971291866028707
1996	8.74384236453202
1997	10.112359550561797
1998	9.548387096774194
1999	9.920634920634921
2000	10.068027210884352
2001	11.218836565096952
2002	12.903225806451612
2003	13.36206896551724
2004	14.890510948905108
2005	13.629402756508421
2006	14.545454545454545
2007	13.629402756508421
2008	13.761467889908257