Year	% of total
1970	28.4588305802723
1971	34.43580705617365
1972	35.378784234117994
1973	36.446835158292515
1974	32.361029694878205
1975	32.40728364301529
1976	35.84197215827286
1977	31.154838968961652
1978	30.290476525792652
1979	28.870668744796685
1980	26.413140122354577
1981	21.752339999585075
1982	20.411306927105247
1983	20.196953073915182
1984	20.871081354446154
1985	21.70861465735116
1986	21.38130024098239
1987	20.711690724629253
1988	21.854329669069582
1989	23.328449546708992
1990	27.168576104746318
1991	26.60178426601784
1992	25.837320574162682
1993	24.922118380062305
1994	23.718439173680185
1995	23.595505617977526
1996	23.568281938325992
1997	23.25249643366619
1998	23.249299719887954
1999	23.451635351426585
2000	23.720608575380357
2001	24.403927068723704
2002	25.03556187766714
2003	25.646551724137932
2004	26.0806916426513
2005	26.671511627906973
2006	27.27272727272727
2007	26.79640718562874
2008	25.553914327917283