Year	% of total
1970	27.72205788381185
1971	27.75255675129121
1972	26.335107948891444
1973	29.352652184342382
1974	30.926511719751744
1975	26.095750984893222
1976	28.699463987350654
1977	28.22667969266407
1978	29.63105342164532
1979	29.21072879087782
1980	30.517435052825043
1981	30.115076944108598
1982	25.335051961723092
1983	24.622288117335025
1984	24.860158350292537
1985	25.3324196559015
1986	25.23358682965161
1987	24.930520122802204
1988	24.8056265649721
1989	23.955912084142298
1990	26.405451448040886
1991	26.36986301369863
1992	23.164918970448046
1993	24.196787148594378
1994	24.17815482502651
1995	22.24744608399546
1996	22.702104097452935
1997	21.948488241881297
1998	20.73310423825888
1999	19.886363636363637
2000	20.782122905027933
2001	21.53325817361894
2002	19.954389965792473
2003	21.262458471760798
2004	19.396051103368176
2005	18.4964200477327
2006	18.712029161603887
2007	17.980295566502463
2008	17.72784019975031