Year	% of total
1970	25.59257511354705
1971	26.80928758332885
1972	28.28020156705301
1973	28.140042023388247
1974	28.545701521329676
1975	28.923936602973704
1976	28.619296152759894
1977	26.59013784520818
1978	27.15124002559614
1979	27.14915843067407
1980	27.3744132265234
1981	28.24299287926439
1982	26.33132951566268
1983	24.510118512032015
1984	23.6286167638209
1985	25.107616523889124
1986	25.39492820141365
1987	25.113851332204835
1988	24.48730775031226
1989	24.41566102319924
1990	0
1991	0
1992	0
1993	0
1994	0
1995	0
1996	0
1997	0
1998	0
1999	0
2000	0
2001	0
2002	0
2003	0
2004	0
2005	0
2006	0
2007	0
2008	0